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MySQL Reference Manual for version 5.0.0-alpha. - 20 MySQL APIs Go to the first, previous, next, last section, table of contents.


20 MySQL APIs

This chapter describes the APIs available for MySQL, where to get them, and how to use them. The C API is the most extensively covered, as it was developed by the MySQL team, and is the basis for most of the other APIs.

20.1 MySQL Program Development Utilities

This section describes some utilities that you may find useful when developing MySQL programs.

msql2mysql
A shell script that converts mSQL programs to MySQL. It doesn't handle every case, but it gives a good start when converting.
mysql_config
A shell script that produces the option values needed when compiling MySQL programs.

20.1.1 msql2mysql, Convert mSQL Programs for Use with MySQL

Initially, the MySQL C API was developed to be very similar to that for the mSQL database system. Because of this, mSQL programs often can be converted relatively easily for use with MySQL by changing the names of the C API functions.

The msql2mysql utility performs the conversion of mSQL C API function calls to their MySQL equivalents. msql2mysql converts the input file in place, so make a copy of the original before converting it. For example, use msql2mysql like this:

shell> cp client-prog.c client-prog.c.orig
shell> msql2mysql client-prog.c
client-prog.c converted

Then examine `client-prog.c' and make any post-conversion revisions that may be necessary.

msql2mysql uses the replace utility to make the function name substitutions. See section 8.13 The replace String-replacement Utility.

20.1.2 mysql_config, Get compile options for compiling clients

mysql_config provides you with useful information for compiling your MySQL client and connecting it to MySQL.

mysql_config supports the following options:

--cflags
Compiler flags to find include files and critical compiler flags and defines used when compiling the libmysqlclient library.
--include
Compiler options to find MySQL include files. (Note that normally you would use --cflags instead of this option.)
--libmysqld-libs, --embedded
Libraries and options required to link with the MySQL embedded server.
--libs
Libraries and options required to link with the MySQL client library.
--libs_r
Libraries and options required to link with the thread-safe MySQL client library.
--port
The default TCP/IP port number, defined when configuring MySQL.
--socket
The default Unix socket file, defined when configuring MySQL.
--version
Version number and version for the MySQL distribution.

If you invoke mysql_config with no options, it displays a list of all options that it supports, and their values:

shell> mysql_config
Usage: /usr/local/mysql/bin/mysql_config [options]
Options:
  --cflags         [-I/usr/local/mysql/include/mysql -mcpu=pentiumpro]
  --include        [-I/usr/local/mysql/include/mysql]
  --libs           [-L/usr/local/mysql/lib/mysql -lmysqlclient -lz
                    -lcrypt -lnsl -lm -L/usr/lib -lssl -lcrypto]
  --libs_r         [-L/usr/local/mysql/lib/mysql -lmysqlclient_r
                    -lpthread -lz -lcrypt -lnsl -lm -lpthread]
  --socket         [/tmp/mysql.sock]
  --port           [3306]
  --version        [4.0.16]
  --libmysqld-libs [-L/usr/local/mysql/lib/mysql -lmysqld -lpthread -lz
                    -lcrypt -lnsl -lm -lpthread -lrt]

You can use mysql_config within a command line to include the value that it displays for a particular option. For example, to compile a MySQL client program, use mysql_config as follows:

CFG=/usr/local/mysql/bin/mysql_config
sh -c "gcc -o progname `$CFG --cflags` progname.c `$CFG --libs`"

When you use mysql_config this way, be sure to invoke it within backtick (``') characters. That tells the shell to execute it and subsitute its output into the surrounding command.

20.2 MySQL C API

The C API code is distributed with MySQL. It is included in the mysqlclient library and allows C programs to access a database.

Many of the clients in the MySQL source distribution are written in C. If you are looking for examples that demonstrate how to use the C API, take a look at these clients. You can find these in the clients directory in the MySQL source distribution.

Most of the other client APIs (all except Connector/J) use the mysqlclient library to communicate with the MySQL server. This means that, for example, you can take advantage of many of the same environment variables that are used by other client programs, because they are referenced from the library. See section 8 MySQL Client and Utility Programs, for a list of these variables.

The client has a maximum communication buffer size. The size of the buffer that is allocated initially (16KB) is automatically increased up to the maximum size (the maximum is 16M). Because buffer sizes are increased only as demand warrants, simply increasing the default maximum limit does not in itself cause more resources to be used. This size check is mostly a check for erroneous queries and communication packets.

The communication buffer must be large enough to contain a single SQL statement (for client-to-server traffic) and one row of returned data (for server-to-client traffic). Each thread's communication buffer is dynamically enlarged to handle any query or row up to the maximum limit. For example, if you have BLOB values that contain up to 16MB of data, you must have a communication buffer limit of at least 16MB (in both server and client). The client's default maximum is 16MB, but the default maximum in the server is 1MB. You can increase this by changing the value of the max_allowed_packet parameter when the server is started. See section 7.5.2 Tuning Server Parameters.

The MySQL server shrinks each communication buffer to net_buffer_length bytes after each query. For clients, the size of the buffer associated with a connection is not decreased until the connection is closed, at which time client memory is reclaimed.

For programming with threads, see section 20.2.14 How to Make a Threaded Client. For creating a stand-alone application which includes the "server" and "client" in the same program (and does not communicate with an external MySQL server), see section 20.2.15 libmysqld, the Embedded MySQL Server Library.

20.2.1 C API Datatypes

MYSQL
This structure represents a handle to one database connection. It is used for almost all MySQL functions.
MYSQL_RES
This structure represents the result of a query that returns rows (SELECT, SHOW, DESCRIBE, EXPLAIN). The information returned from a query is called the result set in the remainder of this section.
MYSQL_ROW
This is a type-safe representation of one row of data. It is currently implemented as an array of counted byte strings. (You cannot treat these as null-terminated strings if field values may contain binary data, because such values may contain null bytes internally.) Rows are obtained by calling mysql_fetch_row().
MYSQL_FIELD
This structure contains information about a field, such as the field's name, type, and size. Its members are described in more detail here. You may obtain the MYSQL_FIELD structures for each field by calling mysql_fetch_field() repeatedly. Field values are not part of this structure; they are contained in a MYSQL_ROW structure.
MYSQL_FIELD_OFFSET
This is a type-safe representation of an offset into a MySQL field list. (Used by mysql_field_seek().) Offsets are field numbers within a row, beginning at zero.
my_ulonglong
The type used for the number of rows and for mysql_affected_rows(), mysql_num_rows(), and mysql_insert_id(). This type provides a range of 0 to 1.84e19. On some systems, attempting to print a value of type my_ulonglong will not work. To print such a value, convert it to unsigned long and use a %lu print format. Example:
printf ("Number of rows: %lu\n", (unsigned long) mysql_num_rows(result));

The MYSQL_FIELD structure contains the members listed here:

char * name
The name of the field, as a null-terminated string.
char * table
The name of the table containing this field, if it isn't a calculated field. For calculated fields, the table value is an empty string.
char * def
The default value of this field, as a null-terminated string. This is set only if you use mysql_list_fields().
enum enum_field_types type
The type of the field. The type value may be one of the following:
Type Value Type Description
FIELD_TYPE_TINY TINYINT field
FIELD_TYPE_SHORT SMALLINT field
FIELD_TYPE_LONG INTEGER field
FIELD_TYPE_INT24 MEDIUMINT field
FIELD_TYPE_LONGLONG BIGINT field
FIELD_TYPE_DECIMAL DECIMAL or NUMERIC field
FIELD_TYPE_FLOAT FLOAT field
FIELD_TYPE_DOUBLE DOUBLE or REAL field
FIELD_TYPE_TIMESTAMP TIMESTAMP field
FIELD_TYPE_DATE DATE field
FIELD_TYPE_TIME TIME field
FIELD_TYPE_DATETIME DATETIME field
FIELD_TYPE_YEAR YEAR field
FIELD_TYPE_STRING CHAR field
FIELD_TYPE_VAR_STRING VARCHAR field
FIELD_TYPE_BLOB BLOB or TEXT field (use max_length to determine the maximum length)
FIELD_TYPE_SET SET field
FIELD_TYPE_ENUM ENUM field
FIELD_TYPE_NULL NULL-type field
FIELD_TYPE_CHAR Deprecated; use FIELD_TYPE_TINY instead
You can use the IS_NUM() macro to test whether a field has a numeric type. Pass the type value to IS_NUM() and it will evaluate to TRUE if the field is numeric:
if (IS_NUM(field->type))
    printf("Field is numeric\n");
unsigned int length
The width of the field, as specified in the table definition.
unsigned int max_length
The maximum width of the field for the result set (the length of the longest field value for the rows actually in the result set). If you use mysql_store_result() or mysql_list_fields(), this contains the maximum length for the field. If you use mysql_use_result(), the value of this variable is zero.
unsigned int flags
Different bit-flags for the field. The flags value may have zero or more of the following bits set:
Flag Value Flag Description
NOT_NULL_FLAG Field can't be NULL
PRI_KEY_FLAG Field is part of a primary key
UNIQUE_KEY_FLAG Field is part of a unique key
MULTIPLE_KEY_FLAG Field is part of a non-unique key
UNSIGNED_FLAG Field has the UNSIGNED attribute
ZEROFILL_FLAG Field has the ZEROFILL attribute
BINARY_FLAG Field has the BINARY attribute
AUTO_INCREMENT_FLAG Field has the AUTO_INCREMENT attribute
ENUM_FLAG Field is an ENUM (deprecated)
SET_FLAG Field is a SET (deprecated)
BLOB_FLAG Field is a BLOB or TEXT (deprecated)
TIMESTAMP_FLAG Field is a TIMESTAMP (deprecated)
Use of the BLOB_FLAG, ENUM_FLAG, SET_FLAG, and TIMESTAMP_FLAG flags is deprecated because they indicate the type of a field rather than an attribute of its type. It is preferable to test field->type against FIELD_TYPE_BLOB, FIELD_TYPE_ENUM, FIELD_TYPE_SET, or FIELD_TYPE_TIMESTAMP instead. The following example illustrates a typical use of the flags value:
if (field->flags & NOT_NULL_FLAG)
    printf("Field can't be null\n");
You may use the following convenience macros to determine the boolean status of the flags value:
Flag Status Description
IS_NOT_NULL(flags) True if this field is defined as NOT NULL
IS_PRI_KEY(flags) True if this field is a primary key
IS_BLOB(flags) True if this field is a BLOB or TEXT (deprecated; test field->type instead)
unsigned int decimals
The number of decimals for numeric fields.

20.2.2 C API Function Overview

The functions available in the C API are summarized here and described in greater detail in a later section. See section 20.2.3 C API Function Descriptions.

Function Description
mysql_affected_rows() Returns the number of rows changed/deleted/inserted by the last UPDATE, DELETE, or INSERT query.
mysql_change_user() Changes user and database on an open connection.
mysql_character_set_name() Returns the name of the default character set for the connection.
mysql_close() Closes a server connection.
mysql_connect() Connects to a MySQL server. This function is deprecated; use mysql_real_connect() instead.
mysql_create_db() Creates a database. This function is deprecated; use the SQL command CREATE DATABASE instead.
mysql_data_seek() Seeks to an arbitrary row number in a query result set.
mysql_debug() Does a DBUG_PUSH with the given string.
mysql_drop_db() Drops a database. This function is deprecated; use the SQL command DROP DATABASE instead.
mysql_dump_debug_info() Makes the server write debug information to the log.
mysql_eof() Determines whether the last row of a result set has been read. This function is deprecated; mysql_errno() or mysql_error() may be used instead.
mysql_errno() Returns the error number for the most recently invoked MySQL function.
mysql_error() Returns the error message for the most recently invoked MySQL function.
mysql_escape_string() Escapes special characters in a string for use in an SQL statement.
mysql_fetch_field() Returns the type of the next table field.
mysql_fetch_field_direct() Returns the type of a table field, given a field number.
mysql_fetch_fields() Returns an array of all field structures.
mysql_fetch_lengths() Returns the lengths of all columns in the current row.
mysql_fetch_row() Fetches the next row from the result set.
mysql_field_seek() Puts the column cursor on a specified column.
mysql_field_count() Returns the number of result columns for the most recent query.
mysql_field_tell() Returns the position of the field cursor used for the last mysql_fetch_field().
mysql_free_result() Frees memory used by a result set.
mysql_get_client_info() Returns client version information as a string.
mysql_get_client_version() Returns client version information as an integer.
mysql_get_host_info() Returns a string describing the connection.
mysql_get_server_version() Returns version number of server as an integer (new in 4.1).
mysql_get_proto_info() Returns the protocol version used by the connection.
mysql_get_server_info() Returns the server version number.
mysql_info() Returns information about the most recently executed query.
mysql_init() Gets or initializes a MYSQL structure.
mysql_insert_id() Returns the ID generated for an AUTO_INCREMENT column by the previous query.
mysql_kill() Kills a given thread.
mysql_list_dbs() Returns database names matching a simple regular expression.
mysql_list_fields() Returns field names matching a simple regular expression.
mysql_list_processes() Returns a list of the current server threads.
mysql_list_tables() Returns table names matching a simple regular expression.
mysql_num_fields() Returns the number of columns in a result set.
mysql_num_rows() Returns the number of rows in a result set.
mysql_options() Sets connect options for mysql_connect().
mysql_ping() Checks whether the connection to the server is working, reconnecting as necessary.
mysql_query() Executes an SQL query specified as a null-terminated string.
mysql_real_connect() Connects to a MySQL server.
mysql_real_escape_string() Escapes special characters in a string for use in an SQL statement, taking into account the current charset of the connection.
mysql_real_query() Executes an SQL query specified as a counted string.
mysql_reload() Tells the server to reload the grant tables.
mysql_row_seek() Seeks to a row offset in a result set, using value returned from mysql_row_tell().
mysql_row_tell() Returns the row cursor position.
mysql_select_db() Selects a database.
mysql_set_server_option() Sets an option for the connection (like multi-statements).
mysql_sqlstate() Returns the SQLSTATE error code for the last error.
mysql_shutdown() Shuts down the database server.
mysql_stat() Returns the server status as a string.
mysql_store_result() Retrieves a complete result set to the client.
mysql_thread_id() Returns the current thread ID.
mysql_thread_safe() Returns 1 if the clients are compiled as thread-safe.
mysql_use_result() Initiates a row-by-row result set retrieval.
mysql_warning_count() Returns the warning count for the previous SQL statement.
mysql_commit() Commits the transaction (new in 4.1).
mysql_rollback() Rolls back the transaction (new in 4.1).
mysql_autocommit() Toggles autocommit mode on/off (new in 4.1).
mysql_more_results() Checks whether any more results exist (new in 4.1).
mysql_next_result() Returns/Initiates the next result in multi-query executions (new in 4.1).

To connect to the server, call mysql_init() to initialize a connection handler, then call mysql_real_connect() with that handler (along with other information such as the hostname, username, and password). Upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1. This flag indicates, in the event that a query cannot be performed because of a lost connection, to try reconnecting to the server before giving up. When you are done with the connection, call mysql_close() to terminate it.

While a connection is active, the client may send SQL queries to the server using mysql_query() or mysql_real_query(). The difference between the two is that mysql_query() expects the query to be specified as a null-terminated string whereas mysql_real_query() expects a counted string. If the string contains binary data (which may include null bytes), you must use mysql_real_query().

For each non-SELECT query (for example, INSERT, UPDATE, DELETE), you can find out how many rows were changed (affected) by calling mysql_affected_rows().

For SELECT queries, you retrieve the selected rows as a result set. (Note that some statements are SELECT-like in that they return rows. These include SHOW, DESCRIBE, and EXPLAIN. They should be treated the same way as SELECT statements.)

There are two ways for a client to process result sets. One way is to retrieve the entire result set all at once by calling mysql_store_result(). This function acquires from the server all the rows returned by the query and stores them in the client. The second way is for the client to initiate a row-by-row result set retrieval by calling mysql_use_result(). This function initializes the retrieval, but does not actually get any rows from the server.

In both cases, you access rows by calling mysql_fetch_row(). With mysql_store_result(), mysql_fetch_row() accesses rows that have already been fetched from the server. With mysql_use_result(), mysql_fetch_row() actually retrieves the row from the server. Information about the size of the data in each row is available by calling mysql_fetch_lengths().

After you are done with a result set, call mysql_free_result() to free the memory used for it.

The two retrieval mechanisms are complementary. Client programs should choose the approach that is most appropriate for their requirements. In practice, clients tend to use mysql_store_result() more commonly.

An advantage of mysql_store_result() is that because the rows have all been fetched to the client, you not only can access rows sequentially, you can move back and forth in the result set using mysql_data_seek() or mysql_row_seek() to change the current row position within the result set. You can also find out how many rows there are by calling mysql_num_rows(). On the other hand, the memory requirements for mysql_store_result() may be very high for large result sets and you are more likely to encounter out-of-memory conditions.

An advantage of mysql_use_result() is that the client requires less memory for the result set because it maintains only one row at a time (and because there is less allocation overhead, mysql_use_result() can be faster). Disadvantages are that you must process each row quickly to avoid tying up the server, you don't have random access to rows within the result set (you can only access rows sequentially), and you don't know how many rows are in the result set until you have retrieved them all. Furthermore, you must retrieve all the rows even if you determine in mid-retrieval that you've found the information you were looking for.

The API makes it possible for clients to respond appropriately to queries (retrieving rows only as necessary) without knowing whether or not the query is a SELECT. You can do this by calling mysql_store_result() after each mysql_query() (or mysql_real_query()). If the result set call succeeds, the query was a SELECT and you can read the rows. If the result set call fails, call mysql_field_count() to determine whether a result was actually to be expected. If mysql_field_count() returns zero, the query returned no data (indicating that it was an INSERT, UPDATE, DELETE, etc.), and was not expected to return rows. If mysql_field_count() is non-zero, the query should have returned rows, but didn't. This indicates that the query was a SELECT that failed. See the description for mysql_field_count() for an example of how this can be done.

Both mysql_store_result() and mysql_use_result() allow you to obtain information about the fields that make up the result set (the number of fields, their names and types, etc.). You can access field information sequentially within the row by calling mysql_fetch_field() repeatedly, or by field number within the row by calling mysql_fetch_field_direct(). The current field cursor position may be changed by calling mysql_field_seek(). Setting the field cursor affects subsequent calls to mysql_fetch_field(). You can also get information for fields all at once by calling mysql_fetch_fields().

For detecting and reporting errors, MySQL provides access to error information by means of the mysql_errno() and mysql_error() functions. These return the error code or error message for the most recently invoked function that can succeed or fail, allowing you to determine when an error occurred and what it was.

20.2.3 C API Function Descriptions

In the descriptions here, a parameter or return value of NULL means NULL in the sense of the C programming language, not a MySQL NULL value.

Functions that return a value generally return a pointer or an integer. Unless specified otherwise, functions returning a pointer return a non-NULL value to indicate success or a NULL value to indicate an error, and functions returning an integer return zero to indicate success or non-zero to indicate an error. Note that ``non-zero'' means just that. Unless the function description says otherwise, do not test against a value other than zero:

if (result)                   /* correct */
    ... error ...

if (result < 0)               /* incorrect */
    ... error ...

if (result == -1)             /* incorrect */
    ... error ...

When a function returns an error, the Errors subsection of the function description lists the possible types of errors. You can find out which of these occurred by calling mysql_errno(). A string representation of the error may be obtained by calling mysql_error().

20.2.3.1 mysql_affected_rows()

my_ulonglong mysql_affected_rows(MYSQL *mysql)

Description

Returns the number of rows changed by the last UPDATE, deleted by the last DELETE or inserted by the last INSERT statement. May be called immediately after mysql_query() for UPDATE, DELETE, or INSERT statements. For SELECT statements, mysql_affected_rows() works like mysql_num_rows().

Return Values

An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records where updated for an UPDATE statement, no rows matched the WHERE clause in the query or that no query has yet been executed. -1 indicates that the query returned an error or that, for a SELECT query, mysql_affected_rows() was called prior to calling mysql_store_result(). Because mysql_affected_rows() returns an unsigned value, you can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).

Errors

None.

Example

mysql_query(&mysql,"UPDATE products SET cost=cost*1.25 WHERE group=10");
printf("%ld products updated",(long) mysql_affected_rows(&mysql));

If one specifies the flag CLIENT_FOUND_ROWS when connecting to mysqld, mysql_affected_rows() will return the number of rows matched by the WHERE statement for UPDATE statements.

Note that when one uses a REPLACE command, mysql_affected_rows() will return 2 if the new row replaced and old row. This is because in this case one row was inserted after the duplicate was deleted.

20.2.3.2 mysql_change_user()

my_bool mysql_change_user(MYSQL *mysql, const char *user, const char *password, const char *db)

Description

Changes the user and causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that do not include an explicit database specifier.

This function was introduced in MySQL Version 3.23.3.

mysql_change_user() fails if the connected user cannot be authenticated or doesn't have permission to use the database. In this case the user and database are not changed

The db parameter may be set to NULL if you don't want to have a default database.

Starting from MySQL 4.0.6 this command will always ROLLBACK any active transactions, close all temporary tables, unlock all locked tables and reset the state as if one had done a new connect. This will happen even if the user didn't change.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

The same that you can get from mysql_real_connect().

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.
ER_UNKNOWN_COM_ERROR
The MySQL server doesn't implement this command (probably an old server).
ER_ACCESS_DENIED_ERROR
The user or password was wrong.
ER_BAD_DB_ERROR
The database didn't exist.
ER_DBACCESS_DENIED_ERROR
The user did not have access rights to the database.
ER_WRONG_DB_NAME
The database name was too long.

Example

if (mysql_change_user(&mysql, "user", "password", "new_database"))
{
   fprintf(stderr, "Failed to change user.  Error: %s\n",
           mysql_error(&mysql));
}

20.2.3.3 mysql_character_set_name()

const char *mysql_character_set_name(MYSQL *mysql)

Description

Returns the default character set for the current connection.

Return Values

The default character set

Errors

None.

20.2.3.4 mysql_close()

void mysql_close(MYSQL *mysql)

Description

Closes a previously opened connection. mysql_close() also deallocates the connection handle pointed to by mysql if the handle was allocated automatically by mysql_init() or mysql_connect().

Return Values

None.

Errors

None.

20.2.3.5 mysql_connect()

MYSQL *mysql_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd)

Description

This function is deprecated. It is preferable to use mysql_real_connect() instead.

mysql_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_connect() must complete successfully before you can execute any of the other API functions, with the exception of mysql_get_client_info().

The meanings of the parameters are the same as for the corresponding parameters for mysql_real_connect() with the difference that the connection parameter may be NULL. In this case the C API allocates memory for the connection structure automatically and frees it when you call mysql_close(). The disadvantage of this approach is that you can't retrieve an error message if the connection fails. (To get error information from mysql_errno() or mysql_error(), you must provide a valid MYSQL pointer.)

Return Values

Same as for mysql_real_connect().

Errors

Same as for mysql_real_connect().

20.2.3.6 mysql_create_db()

int mysql_create_db(MYSQL *mysql, const char *db)

Description

Creates the database named by the db parameter.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL CREATE DATABASE statement instead.

Return Values

Zero if the database was created successfully. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

Example

if(mysql_create_db(&mysql, "my_database"))
{
   fprintf(stderr, "Failed to create new database.  Error: %s\n",
           mysql_error(&mysql));
}

20.2.3.7 mysql_data_seek()

void mysql_data_seek(MYSQL_RES *result, my_ulonglong offset)

Description

Seeks to an arbitrary row in a query result set. The offset value is a row number and should be in the range from 0 to mysql_num_rows(stmt)-1.

This function requires that the result set structure contains the entire result of the query, so mysql_data_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().

Return Values

None.

Errors

None.

20.2.3.8 mysql_debug()

void mysql_debug(const char *debug)

Description

Does a DBUG_PUSH with the given string. mysql_debug() uses the Fred Fish debug library. To use this function, you must compile the client library to support debugging. See section D.1 Debugging a MySQL server. See section D.2 Debugging a MySQL client.

Return Values

None.

Errors

None.

Example

The call shown here causes the client library to generate a trace file in `/tmp/client.trace' on the client machine:

mysql_debug("d:t:O,/tmp/client.trace");

20.2.3.9 mysql_drop_db()

int mysql_drop_db(MYSQL *mysql, const char *db)

Description

Drops the database named by the db parameter.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL DROP DATABASE statement instead.

Return Values

Zero if the database was dropped successfully. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

Example

if(mysql_drop_db(&mysql, "my_database"))
  fprintf(stderr, "Failed to drop the database: Error: %s\n",
          mysql_error(&mysql));

20.2.3.10 mysql_dump_debug_info()

int mysql_dump_debug_info(MYSQL *mysql)

Description

Instructs the server to write some debug information to the log. For this to work, the connected user must have the SUPER privilege.

Return Values

Zero if the command was successful. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.11 mysql_eof()

my_bool mysql_eof(MYSQL_RES *result)

Description

This function is deprecated. mysql_errno() or mysql_error() may be used instead.

mysql_eof() determines whether the last row of a result set has been read.

If you acquire a result set from a successful call to mysql_store_result(), the client receives the entire set in one operation. In this case, a NULL return from mysql_fetch_row() always means the end of the result set has been reached and it is unnecessary to call mysql_eof(). When used with mysql_store_result(), mysql_eof() will always return true.

On the other hand, if you use mysql_use_result() to initiate a result set retrieval, the rows of the set are obtained from the server one by one as you call mysql_fetch_row() repeatedly. Because an error may occur on the connection during this process, a NULL return value from mysql_fetch_row() does not necessarily mean the end of the result set was reached normally. In this case, you can use mysql_eof() to determine what happened. mysql_eof() returns a non-zero value if the end of the result set was reached and zero if an error occurred.

Historically, mysql_eof() predates the standard MySQL error functions mysql_errno() and mysql_error(). Because those error functions provide the same information, their use is preferred over mysql_eof(), which is now deprecated. (In fact, they provide more information, because mysql_eof() returns only a boolean value whereas the error functions indicate a reason for the error when one occurs.)

Return Values

Zero if no error occurred. Non-zero if the end of the result set has been reached.

Errors

None.

Example

The following example shows how you might use mysql_eof():

mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
    // do something with data
}
if(!mysql_eof(result))  // mysql_fetch_row() failed due to an error
{
    fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}

However, you can achieve the same effect with the standard MySQL error functions:

mysql_query(&mysql,"SELECT * FROM some_table");
result = mysql_use_result(&mysql);
while((row = mysql_fetch_row(result)))
{
    // do something with data
}
if(mysql_errno(&mysql))  // mysql_fetch_row() failed due to an error
{
    fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
}

20.2.3.12 mysql_errno()

unsigned int mysql_errno(MYSQL *mysql)

Description

For the connection specified by mysql, mysql_errno() returns the error code for the most recently invoked API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL `errmsg.h' header file. Server error message numbers are listed in `mysqld_error.h'. In the MySQL source distribution you can find a complete list of error messages and error numbers in the file `Docs/mysqld_error.txt'. The server error codes also are listed at section 21.1 Error Returns.

Note that some functions like mysql_fetch_row() don't set mysql_errno() if they succeed.

A rule of thumb is that all functions that have to ask the server for information will reset mysql_errno() if they succeed.

Return Values

An error code value for the last mysql_xxx call, if it failed. zero means no error occurred.

Errors

None.

20.2.3.13 mysql_error()

const char *mysql_error(MYSQL *mysql)

Description

For the connection specified by mysql, mysql_error() returns a null-terminated string containing the error message for the most recently invoked API function that failed. If a function didn't fail, the return value of mysql_error() may be the previous error or an empty string to indicate no error.

A rule of thumb is that all functions that have to ask the server for information will reset mysql_error() if they succeed.

For functions that resets mysql_errno, the following two tests are equivalent:

if(mysql_errno(&mysql))
{
    // an error occurred
}

if(mysql_error(&mysql)[0] != '\0')
{
    // an error occurred
}

The language of the client error messages may be changed by recompiling the MySQL client library. Currently you can choose error messages in several different languages. See section 5.7.2 Setting the Error Message Language.

Return Values

A null-terminated character string that describes the error. An empty string if no error occurred.

Errors

None.

20.2.3.14 mysql_escape_string()

You should use mysql_real_escape_string() instead!

This function is identical to mysql_real_escape_string() except that mysql_real_escape_string() takes a connection handler as its first argument and escapes the string according to the current character set. mysql_escape_string() does not take a connection argument and does not respect the current charset setting.

20.2.3.15 mysql_fetch_field()

MYSQL_FIELD *mysql_fetch_field(MYSQL_RES *result)

Description

Returns the definition of one column of a result set as a MYSQL_FIELD structure. Call this function repeatedly to retrieve information about all columns in the result set. mysql_fetch_field() returns NULL when no more fields are left.

mysql_fetch_field() is reset to return information about the first field each time you execute a new SELECT query. The field returned by mysql_fetch_field() is also affected by calls to mysql_field_seek().

If you've called mysql_query() to perform a SELECT on a table but have not called mysql_store_result(), MySQL returns the default blob length (8KB) if you call mysql_fetch_field() to ask for the length of a BLOB field. (The 8KB size is chosen because MySQL doesn't know the maximum length for the BLOB. This should be made configurable sometime.) Once you've retrieved the result set, field->max_length contains the length of the largest value for this column in the specific query.

Return Values

The MYSQL_FIELD structure for the current column. NULL if no columns are left.

Errors

None.

Example

MYSQL_FIELD *field;

while((field = mysql_fetch_field(result)))
{
    printf("field name %s\n", field->name);
}

20.2.3.16 mysql_fetch_fields()

MYSQL_FIELD *mysql_fetch_fields(MYSQL_RES *result)

Description

Returns an array of all MYSQL_FIELD structures for a result set. Each structure provides the field definition for one column of the result set.

Return Values

An array of MYSQL_FIELD structures for all columns of a result set.

Errors

None.

Example

unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *fields;

num_fields = mysql_num_fields(result);
fields = mysql_fetch_fields(result);
for(i = 0; i < num_fields; i++)
{
   printf("Field %u is %s\n", i, fields[i].name);
}

20.2.3.17 mysql_fetch_field_direct()

MYSQL_FIELD *mysql_fetch_field_direct(MYSQL_RES *result, unsigned int fieldnr)

Description

Given a field number fieldnr for a column within a result set, returns that column's field definition as a MYSQL_FIELD structure. You may use this function to retrieve the definition for an arbitrary column. The value of fieldnr should be in the range from 0 to mysql_num_fields(result)-1.

Return Values

The MYSQL_FIELD structure for the specified column.

Errors

None.

Example

unsigned int num_fields;
unsigned int i;
MYSQL_FIELD *field;

num_fields = mysql_num_fields(result);
for(i = 0; i < num_fields; i++)
{
    field = mysql_fetch_field_direct(result, i);
    printf("Field %u is %s\n", i, field->name);
}

20.2.3.18 mysql_fetch_lengths()

unsigned long *mysql_fetch_lengths(MYSQL_RES *result)

Description

Returns the lengths of the columns of the current row within a result set. If you plan to copy field values, this length information is also useful for optimization, because you can avoid calling strlen(). In addition, if the result set contains binary data, you must use this function to determine the size of the data, because strlen() returns incorrect results for any field containing null characters.

The length for empty columns and for columns containing NULL values is zero. To see how to distinguish these two cases, see the description for mysql_fetch_row().

Return Values

An array of unsigned long integers representing the size of each column (not including any terminating null characters). NULL if an error occurred.

Errors

mysql_fetch_lengths() is valid only for the current row of the result set. It returns NULL if you call it before calling mysql_fetch_row() or after retrieving all rows in the result.

Example

MYSQL_ROW row;
unsigned long *lengths;
unsigned int num_fields;
unsigned int i;

row = mysql_fetch_row(result);
if (row)
{
    num_fields = mysql_num_fields(result);
    lengths = mysql_fetch_lengths(result);
    for(i = 0; i < num_fields; i++)
    {
         printf("Column %u is %lu bytes in length.\n", i, lengths[i]);
    }
}

20.2.3.19 mysql_fetch_row()

MYSQL_ROW mysql_fetch_row(MYSQL_RES *result)

Description

Retrieves the next row of a result set. When used after mysql_store_result(), mysql_fetch_row() returns NULL when there are no more rows to retrieve. When used after mysql_use_result(), mysql_fetch_row() returns NULL when there are no more rows to retrieve or if an error occurred.

The number of values in the row is given by mysql_num_fields(result). If row holds the return value from a call to mysql_fetch_row(), pointers to the values are accessed as row[0] to row[mysql_num_fields(result)-1]. NULL values in the row are indicated by NULL pointers.

The lengths of the field values in the row may be obtained by calling mysql_fetch_lengths(). Empty fields and fields containing NULL both have length 0; you can distinguish these by checking the pointer for the field value. If the pointer is NULL, the field is NULL; otherwise, the field is empty.

Return Values

A MYSQL_ROW structure for the next row. NULL if there are no more rows to retrieve or if an error occurred.

Errors

Note that error is not reset between calls to mysql_fetch_row()

CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

Example

MYSQL_ROW row;
unsigned int num_fields;
unsigned int i;

num_fields = mysql_num_fields(result);
while ((row = mysql_fetch_row(result)))
{
   unsigned long *lengths;
   lengths = mysql_fetch_lengths(result);
   for(i = 0; i < num_fields; i++)
   {
       printf("[%.*s] ", (int) lengths[i], row[i] ? row[i] : "NULL");
   }
   printf("\n");
}

20.2.3.20 mysql_field_count()

unsigned int mysql_field_count(MYSQL *mysql)

If you are using a version of MySQL earlier than Version 3.22.24, you should use unsigned int mysql_num_fields(MYSQL *mysql) instead.

Description

Returns the number of columns for the most recent query on the connection.

The normal use of this function is when mysql_store_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a non-empty result. This allows the client program to take proper action without knowing whether the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.

See section 20.2.12.1 Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success.

Return Values

An unsigned integer representing the number of fields in a result set.

Errors

None.

Example

MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;

if (mysql_query(&mysql,query_string))
{
    // error
}
else // query succeeded, process any data returned by it
{
    result = mysql_store_result(&mysql);
    if (result)  // there are rows
    {
        num_fields = mysql_num_fields(result);
        // retrieve rows, then call mysql_free_result(result)
    }
    else  // mysql_store_result() returned nothing; should it have?
    {
        if(mysql_field_count(&mysql) == 0)
        {
            // query does not return data
            // (it was not a SELECT)
            num_rows = mysql_affected_rows(&mysql);
        }
        else // mysql_store_result() should have returned data
        {
            fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
        }
    }
}

An alternative is to replace the mysql_field_count(&mysql) call with mysql_errno(&mysql). In this case, you are checking directly for an error from mysql_store_result() rather than inferring from the value of mysql_field_count() whether the statement was a SELECT.

20.2.3.21 mysql_field_seek()

MYSQL_FIELD_OFFSET mysql_field_seek(MYSQL_RES *result, MYSQL_FIELD_OFFSET offset)

Description

Sets the field cursor to the given offset. The next call to mysql_fetch_field() will retrieve the field definition of the column associated with that offset.

To seek to the beginning of a row, pass an offset value of zero.

Return Values

The previous value of the field cursor.

Errors

None.

20.2.3.22 mysql_field_tell()

MYSQL_FIELD_OFFSET mysql_field_tell(MYSQL_RES *result)

Description

Returns the position of the field cursor used for the last mysql_fetch_field(). This value can be used as an argument to mysql_field_seek().

Return Values

The current offset of the field cursor.

Errors

None.

20.2.3.23 mysql_free_result()

void mysql_free_result(MYSQL_RES *result)

Description

Frees the memory allocated for a result set by mysql_store_result(), mysql_use_result(), mysql_list_dbs(), etc. When you are done with a result set, you must free the memory it uses by calling mysql_free_result().

Do not attempt to access a result set after freeing it.

Return Values

None.

Errors

None.

20.2.3.24 mysql_get_client_info()

char *mysql_get_client_info(void)

Description

Returns a string that represents the client library version.

Return Values

A character string that represents the MySQL client library version.

Errors

None.

20.2.3.25 mysql_get_client_version()

unsigned long mysql_get_client_version(void)

Description

Returns an integer that represents the client library version. The value has the format XYYZZ where X is the major version, YY is the release level, and ZZ is the version number within the release level. For example, a value of 40102 represents a client library version of 4.1.2.

Return Values

An integer that represents the MySQL client library version.

Errors

None.

20.2.3.26 mysql_get_host_info()

char *mysql_get_host_info(MYSQL *mysql)

Description

Returns a string describing the type of connection in use, including the server hostname.

Return Values

A character string representing the server hostname and the connection type.

Errors

None.

20.2.3.27 mysql_get_proto_info()

unsigned int mysql_get_proto_info(MYSQL *mysql)

Description

Returns the protocol version used by current connection.

Return Values

An unsigned integer representing the protocol version used by the current connection.

Errors

None.

20.2.3.28 mysql_get_server_info()

char *mysql_get_server_info(MYSQL *mysql)

Description

Returns a string that represents the server version number.

Return Values

A character string that represents the server version number.

Errors

None.

20.2.3.29 mysql_get_server_version()

unsigned long mysql_get_server_version(MYSQL *mysql)

Description

Returns version number of server as an integer (new in 4.1).

Return Values

A number that represents the MySQL server version in format:

main_version*10000 + minor_version *100 + sub_version

For example, 4.1.0 is returned as 40100.

This is useful to quickly determine the version of the server in a client program to know if some capability exits.

Errors

None.

20.2.3.30 mysql_info()

char *mysql_info(MYSQL *mysql)

Description

Retrieves a string providing information about the most recently executed query, but only for the statements listed here. For other statements, mysql_info() returns NULL. The format of the string varies depending on the type of query, as described here. The numbers are illustrative only; the string will contain values appropriate for the query.

INSERT INTO ... SELECT ...
String format: Records: 100 Duplicates: 0 Warnings: 0
INSERT INTO ... VALUES (...),(...),(...)...
String format: Records: 3 Duplicates: 0 Warnings: 0
LOAD DATA INFILE ...
String format: Records: 1 Deleted: 0 Skipped: 0 Warnings: 0
ALTER TABLE
String format: Records: 3 Duplicates: 0 Warnings: 0
UPDATE
String format: Rows matched: 40 Changed: 40 Warnings: 0

Note that mysql_info() returns a non-NULL value for INSERT ... VALUES only for the multiple-row form of the statement (that is, only if multiple value lists are specified).

Return Values

A character string representing additional information about the most recently executed query. NULL if no information is available for the query.

Errors

None.

20.2.3.31 mysql_init()

MYSQL *mysql_init(MYSQL *mysql)

Description

Allocates or initializes a MYSQL object suitable for mysql_real_connect(). If mysql is a NULL pointer, the function allocates, initializes, and returns a new object. Otherwise, the object is initialized and the address of the object is returned. If mysql_init() allocates a new object, it will be freed when mysql_close() is called to close the connection.

Return Values

An initialized MYSQL* handle. NULL if there was insufficient memory to allocate a new object.

Errors

In case of insufficient memory, NULL is returned.

20.2.3.32 mysql_insert_id()

my_ulonglong mysql_insert_id(MYSQL *mysql)

Description

Returns the value generated for an AUTO_INCREMENT column by the previous INSERT or UPDATE statement. Use this function after you have performed an INSERT statement into a table that contains an AUTO_INCREMENT field.

More precisely, mysql_insert_id() is updated under these conditions:

  • INSERT statements that store a value into an AUTO_INCREMENT column. This is true whether the value is automatically generated by storing the special values NULL or 0 into the column, or is an explicit non-special value.
  • In the case of a multi-row INSERT statement, mysql_insert_id() returns the first automatically generated AUTO_INCREMENT value; if no such value is generated, it returns the last last explicit value inserted into the AUTO_INCREMENT column.
  • INSERT statements that generate an AUTO_INCREMENT value by inserting LAST_INSERT_ID(expr) into any column.
  • INSERT statements that generate an AUTO_INCREMENT value by updating any column to LAST_INSERT_ID(expr).
  • The value of mysql_insert_id() is not affected by statements such as SELECT that return a result set.
  • If the previous statement returned an error, the value of mysql_insert_id() is undefined.

Note that mysql_insert_id() returns 0 if the previous statement does not use an AUTO_INCREMENT value. If you need to save the value for later, be sure to call mysql_insert_id() immediately after the statement that generates the value.

The value of mysql_insert_id() is affected only by statements issued within the current client connection. It is not affected by statements issued by other clients.

See section 13.8.3 Information Functions.

Also note that the value of the SQL LAST_INSERT_ID() function always contains the most recently generated AUTO_INCREMENT value, and is not reset between statements because the value of that function is maintained in the server. Another difference is that LAST_INSERT_ID() is not updated if you set an AUTO_INCREMENT column to a specific non-special value.

The reason for the difference between LAST_INSERT_ID() and mysql_insert_id() is that LAST_INSERT_ID() is made easy to use in scripts while mysql_insert_id() tries to provide a little more exact information of what happens to the AUTO_INCREMENT column.

Return Values

Described in the preceding discussion.

Errors

None.

20.2.3.33 mysql_kill()

int mysql_kill(MYSQL *mysql, unsigned long pid)

Description

Asks the server to kill the thread specified by pid.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.34 mysql_list_dbs()

MYSQL_RES *mysql_list_dbs(MYSQL *mysql, const char *wild)

Description

Returns a result set consisting of database names on the server that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters `%' or `_', or may be a NULL pointer to match all databases. Calling mysql_list_dbs() is similar to executing the query SHOW databases [LIKE wild].

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_OUT_OF_MEMORY
Out of memory.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.35 mysql_list_fields()

MYSQL_RES *mysql_list_fields(MYSQL *mysql, const char *table, const char *wild)

Description

Returns a result set consisting of field names in the given table that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters `%' or `_', or may be a NULL pointer to match all fields. Calling mysql_list_fields() is similar to executing the query SHOW COLUMNS FROM tbl_name [LIKE wild].

Note that it's recommended that you use SHOW COLUMNS FROM tbl_name instead of mysql_list_fields().

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.36 mysql_list_processes()

MYSQL_RES *mysql_list_processes(MYSQL *mysql)

Description

Returns a result set describing the current server threads. This is the same kind of information as that reported by mysqladmin processlist or a SHOW PROCESSLIST query.

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.37 mysql_list_tables()

MYSQL_RES *mysql_list_tables(MYSQL *mysql, const char *wild)

Description

Returns a result set consisting of table names in the current database that match the simple regular expression specified by the wild parameter. wild may contain the wildcard characters `%' or `_', or may be a NULL pointer to match all tables. Calling mysql_list_tables() is similar to executing the query SHOW tables [LIKE wild].

You must free the result set with mysql_free_result().

Return Values

A MYSQL_RES result set for success. NULL if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.38 mysql_num_fields()

unsigned int mysql_num_fields(MYSQL_RES *result)

Or:

unsigned int mysql_num_fields(MYSQL *mysql)

The second form doesn't work on MySQL Version 3.22.24 or newer. To pass a MYSQL* argument, you must use unsigned int mysql_field_count(MYSQL *mysql) instead.

Description

Returns the number of columns in a result set.

Note that you can get the number of columns either from a pointer to a result set or to a connection handle. You would use the connection handle if mysql_store_result() or mysql_use_result() returned NULL (and thus you have no result set pointer). In this case, you can call mysql_field_count() to determine whether mysql_store_result() should have produced a non-empty result. This allows the client program to take proper action without knowing whether or not the query was a SELECT (or SELECT-like) statement. The example shown here illustrates how this may be done.

See section 20.2.12.1 Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success.

Return Values

An unsigned integer representing the number of fields in a result set.

Errors

None.

Example

MYSQL_RES *result;
unsigned int num_fields;
unsigned int num_rows;

if (mysql_query(&mysql,query_string))
{
    // error
}
else // query succeeded, process any data returned by it
{
    result = mysql_store_result(&mysql);
    if (result)  // there are rows
    {
        num_fields = mysql_num_fields(result);
        // retrieve rows, then call mysql_free_result(result)
    }
    else  // mysql_store_result() returned nothing; should it have?
    {
        if (mysql_errno(&mysql))
        {
           fprintf(stderr, "Error: %s\n", mysql_error(&mysql));
        }
        else if (mysql_field_count(&mysql) == 0)
        {
            // query does not return data
            // (it was not a SELECT)
            num_rows = mysql_affected_rows(&mysql);
        }
    }
}

An alternative (if you know that your query should have returned a result set) is to replace the mysql_errno(&mysql) call with a check whether mysql_field_count(&mysql) is = 0. This will happen only if something went wrong.

20.2.3.39 mysql_num_rows()

my_ulonglong mysql_num_rows(MYSQL_RES *result)

Description

Returns the number of rows in the result set.

The use of mysql_num_rows() depends on whether you use mysql_store_result() or mysql_use_result() to return the result set. If you use mysql_store_result(), mysql_num_rows() may be called immediately. If you use mysql_use_result(), mysql_num_rows() will not return the correct value until all the rows in the result set have been retrieved.

Return Values

The number of rows in the result set.

Errors

None.

20.2.3.40 mysql_options()

int mysql_options(MYSQL *mysql, enum mysql_option option, const char *arg)

Description

Can be used to set extra connect options and affect behavior for a connection. This function may be called multiple times to set several options.

mysql_options() should be called after mysql_init() and before mysql_connect() or mysql_real_connect().

The option argument is the option that you want to set; the arg argument is the value for the option. If the option is an integer, then arg should point to the value of the integer.

Possible options values:

Option Argument Type Function
MYSQL_OPT_CONNECT_TIMEOUT unsigned int * Connect timeout in seconds.
MYSQL_OPT_READ_TIMEOUT unsigned int * Timeout for reads from server (works currently only on Windows on TCP/IP connections)
MYSQL_OPT_WRITE_TIMEOUT unsigned int * Timeout for writes to server (works currently only on Windows on TCP/IP connections)
MYSQL_OPT_COMPRESS Not used Use the compressed client/server protocol.
MYSQL_OPT_LOCAL_INFILE optional pointer to uint If no pointer is given or if pointer points to an unsigned int != 0 the command LOAD LOCAL INFILE is enabled.
MYSQL_OPT_NAMED_PIPE Not used Use named pipes to connect to a MySQL server on NT.
MYSQL_INIT_COMMAND char * Command to execute when connecting to the MySQL server. Will automatically be re-executed when reconnecting.
MYSQL_READ_DEFAULT_FILE char * Read options from the named option file instead of from `my.cnf'.
MYSQL_READ_DEFAULT_GROUP char * Read options from the named group from `my.cnf' or the file specified with MYSQL_READ_DEFAULT_FILE.
MYSQL_OPT_PROTOCOL unsigned int * Type of protocol to use. Should be one of the enum values of mysql_protocol_type defined in `mysql.h'.
MYSQL_SHARED_MEMORY_BASE_NAME char* Named of of shared memory object for communication to server. Should be same as the option -shared-memory-base-name used for the mysqld server you want's to connect to.

Note that the group client is always read if you use MYSQL_READ_DEFAULT_FILE or MYSQL_READ_DEFAULT_GROUP.

The specified group in the option file may contain the following options:

Option Description
connect-timeout Connect timeout in seconds. On Linux this timeout is also used for waiting for the first answer from the server.
compress Use the compressed client/server protocol.
database Connect to this database if no database was specified in the connect command.
debug Debug options.
disable-local-infile Disable use of LOAD DATA LOCAL.
host Default hostname.
init-command Command to execute when connecting to MySQL server. Will automatically be re-executed when reconnecting.
interactive-timeout Same as specifying CLIENT_INTERACTIVE to mysql_real_connect(). See section 20.2.3.43 mysql_real_connect().
local-infile[=(0|1)] If no argument or argument != 0 then enable use of LOAD DATA LOCAL.
max_allowed_packet Max size of packet client can read from server.
password Default password.
pipe Use named pipes to connect to a MySQL server on NT.
protocol={TCP | SOCKET | PIPE | MEMORY} The protocol to use when connecting to server (New in 4.1)
port Default port number.
return-found-rows Tell mysql_info() to return found rows instead of updated rows when using UPDATE.
shared-memory-base-name=name Shared memory name to use to connect to server (default is "MySQL"). New in MySQL 4.1.
socket Default socket file.
user Default user.

Note that timeout has been replaced by connect-timeout, but timeout will still work for a while.

For more information about option files, see section 4.3.2 Using Option Files.

Return Values

Zero for success. Non-zero if you used an unknown option.

Example

MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_OPT_COMPRESS,0);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"odbc");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

This code requests the client to use the compressed client/server protocol and read the additional options from the odbc section in the `my.cnf' file.

20.2.3.41 mysql_ping()

int mysql_ping(MYSQL *mysql)

Description

Checks whether the connection to the server is working. If it has gone down, an automatic reconnection is attempted.

This function can be used by clients that remain idle for a long while, to check whether the server has closed the connection and reconnect if necessary.

Return Values

Zero if the server is alive. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.42 mysql_query()

int mysql_query(MYSQL *mysql, const char *query)

Description

Executes the SQL query pointed to by the null-terminated string query. The query must consist of a single SQL statement. You should not add a terminating semicolon (`;') or \g to the statement.

mysql_query() cannot be used for queries that contain binary data; you should use mysql_real_query() instead. (Binary data may contain the `\0' character, which mysql_query() interprets as the end of the query string.)

If you want to know if the query should return a result set or not, you can use mysql_field_count() to check for this. See section 20.2.3.20 mysql_field_count().

Return Values

Zero if the query was successful. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.43 mysql_real_connect()

MYSQL *mysql_real_connect(MYSQL *mysql, const char *host, const char *user, const char *passwd, const char *db, unsigned int port, const char *unix_socket, unsigned long client_flag)

Description

mysql_real_connect() attempts to establish a connection to a MySQL database engine running on host. mysql_real_connect() must complete successfully before you can execute any of the other API functions, with the exception of mysql_get_client_info().

The parameters are specified as follows:

  • The first parameter should be the address of an existing MYSQL structure. Before calling mysql_real_connect() you must call mysql_init() to initialize the MYSQL structure. You can change a lot of connect options with the mysql_options() call. See section 20.2.3.40 mysql_options().
  • The value of host may be either a hostname or an IP address. If host is NULL or the string "localhost", a connection to the local host is assumed. If the OS supports sockets (Unix) or named pipes (Windows), they are used instead of TCP/IP to connect to the server.
  • The user parameter contains the user's MySQL login ID. If user is NULL or the empty string "", the current user is assumed. Under Unix, this is the current login name. Under Windows ODBC, the current username must be specified explicitly. See section 20.3.2 How to Fill in the Various Fields in the ODBC Administrator Program.
  • The passwd parameter contains the password for user. If passwd is NULL, only entries in the user table for the user that have a blank (empty) password field will be checked for a match. This allows the database administrator to set up the MySQL privilege system in such a way that users get different privileges depending on whether or not they have specified a password. Note: Do not attempt to encrypt the password before calling mysql_real_connect(); password encryption is handled automatically by the client API.
  • db is the database name. If db is not NULL, the connection will set the default database to this value.
  • If port is not 0, the value will be used as the port number for the TCP/IP connection. Note that the host parameter determines the type of the connection.
  • If unix_socket is not NULL, the string specifies the socket or named pipe that should be used. Note that the host parameter determines the type of the connection.
  • The value of client_flag is usually 0, but can be set to a combination of the following flags in very special circumstances:
    Flag Name Flag Nescription
    CLIENT_COMPRESS Use compression protocol.
    CLIENT_FOUND_ROWS Return the number of found (matched) rows, not the number of affected rows.
    CLIENT_IGNORE_SPACE Allow spaces after function names. Makes all functions names reserved words.
    CLIENT_INTERACTIVE Allow interactive_timeout seconds (instead of wait_timeout seconds) of inactivity before closing the connection. The client's session wait_timeout variable will be set to the value of the session interactive_timeout variable.
    CLIENT_LOCAL_FILES Enable LOAD DATA LOCAL handling.
    CLIENT_MULTI_STATEMENTS Tell the server that the client may send multi-row-queries (separated with `;'). If this flag is not set, multi-row-queries are disabled. New in 4.1.
    CLIENT_MULTI_RESULTS Tell the server that the client can handle multiple-result sets from multi-queries or stored procedures. This is automatically set if CLIENT_MULTI_STATEMENTS is set. New in 4.1.
    CLIENT_NO_SCHEMA Don't allow the db_name.tbl_name.col_name syntax. This is for ODBC. It causes the parser to generate an error if you use that syntax, which is useful for trapping bugs in some ODBC programs.
    CLIENT_ODBC The client is an ODBC client. This changes mysqld to be more ODBC-friendly.
    CLIENT_SSL Use SSL (encrypted protocol). This option should not be set by application programs; it is set internally in the client library.

Return Values

A MYSQL* connection handle if the connection was successful, NULL if the connection was unsuccessful. For a successful connection, the return value is the same as the value of the first parameter.

Errors

CR_CONN_HOST_ERROR
Failed to connect to the MySQL server.
CR_CONNECTION_ERROR
Failed to connect to the local MySQL server.
CR_IPSOCK_ERROR
Failed to create an IP socket.
CR_OUT_OF_MEMORY
Out of memory.
CR_SOCKET_CREATE_ERROR
Failed to create a Unix socket.
CR_UNKNOWN_HOST
Failed to find the IP address for the hostname.
CR_VERSION_ERROR
A protocol mismatch resulted from attempting to connect to a server with a client library that uses a different protocol version. This can happen if you use a very old client library to connect to a new server that wasn't started with the --old-protocol option.
CR_NAMEDPIPEOPEN_ERROR
Failed to create a named pipe on Windows.
CR_NAMEDPIPEWAIT_ERROR
Failed to wait for a named pipe on Windows.
CR_NAMEDPIPESETSTATE_ERROR
Failed to get a pipe handler on Windows.
CR_SERVER_LOST
If connect_timeout > 0 and it took longer than connect_timeout seconds to connect to the server or if the server died while executing the init-command.

Example

MYSQL mysql;

mysql_init(&mysql);
mysql_options(&mysql,MYSQL_READ_DEFAULT_GROUP,"your_prog_name");
if (!mysql_real_connect(&mysql,"host","user","passwd","database",0,NULL,0))
{
    fprintf(stderr, "Failed to connect to database: Error: %s\n",
          mysql_error(&mysql));
}

By using mysql_options() the MySQL library will read the [client] and [your_prog_name] sections in the `my.cnf' file which will ensure that your program will work, even if someone has set up MySQL in some non-standard way.

Note that upon connection, mysql_real_connect() sets the reconnect flag (part of the MYSQL structure) to a value of 1. This flag indicates, in the event that a query cannot be performed because of a lost connection, to try reconnecting to the server before giving up.

20.2.3.44 mysql_real_escape_string()

unsigned long mysql_real_escape_string(MYSQL *mysql, char *to, const char *from, unsigned long length)

Description

This function is used to create a legal SQL string that you can use in a SQL statement. See section 10.1.1 Strings.

The string in from is encoded to an escaped SQL string, taking into account the current character set of the connection. The result is placed in to and a terminating null byte is appended. Characters encoded are NUL (ASCII 0), `\n', `\r', `\', `'', `"', and Control-Z (see section 10.1 Literal Values). (Strictly speaking, MySQL requires only that backslash and the quote character used to quote the string in the query be escaped. This function quotes the other characters to make them easier to read in log files.)

The string pointed to by from must be length bytes long. You must allocate the to buffer to be at least length*2+1 bytes long. (In the worst case, each character may need to be encoded as using two bytes, and you need room for the terminating null byte.) When mysql_real_escape_string() returns, the contents of to will be a null-terminated string. The return value is the length of the encoded string, not including the terminating null character.

Example

char query[1000],*end;

end = strmov(query,"INSERT INTO test_table values(");
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"What's this",11);
*end++ = '\'';
*end++ = ',';
*end++ = '\'';
end += mysql_real_escape_string(&mysql, end,"binary data: \0\r\n",16);
*end++ = '\'';
*end++ = ')';

if (mysql_real_query(&mysql,query,(unsigned int) (end - query)))
{
   fprintf(stderr, "Failed to insert row, Error: %s\n",
           mysql_error(&mysql));
}

The strmov() function used in the example is included in the mysqlclient library and works like strcpy() but returns a pointer to the terminating null of the first parameter.

Return Values

The length of the value placed into to, not including the terminating null character.

Errors

None.

20.2.3.45 mysql_real_query()

int mysql_real_query(MYSQL *mysql, const char *query, unsigned long length)

Description

Executes the SQL query pointed to by query, which should be a string length bytes long. The query must consist of a single SQL statement. You should not add a terminating semicolon (`;') or \g to the statement.

You must use mysql_real_query() rather than mysql_query() for queries that contain binary data, because binary data may contain the `\0' character. In addition, mysql_real_query() is faster than mysql_query() because it does not call strlen() on the query string.

If you want to know if the query should return a result set or not, you can use mysql_field_count() to check for this. See section 20.2.3.20 mysql_field_count().

Return Values

Zero if the query was successful. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.46 mysql_reload()

int mysql_reload(MYSQL *mysql)

Description

Asks the MySQL server to reload the grant tables. The connected user must have the RELOAD privilege.

This function is deprecated. It is preferable to use mysql_query() to issue an SQL FLUSH PRIVILEGES statement instead.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.47 mysql_row_seek()

MYSQL_ROW_OFFSET mysql_row_seek(MYSQL_RES *result, MYSQL_ROW_OFFSET offset)

Description

Sets the row cursor to an arbitrary row in a query result set. The offset value is a row offset that should be a value returned from mysql_row_tell() or from mysql_row_seek(). This value is not a row number; if you want to seek to a row within a result set by number, use mysql_data_seek() instead.

This function requires that the result set structure contains the entire result of the query, so mysql_row_seek() may be used only in conjunction with mysql_store_result(), not with mysql_use_result().

Return Values

The previous value of the row cursor. This value may be passed to a subsequent call to mysql_row_seek().

Errors

None.

20.2.3.48 mysql_row_tell()

MYSQL_ROW_OFFSET mysql_row_tell(MYSQL_RES *result)

Description

Returns the current position of the row cursor for the last mysql_fetch_row(). This value can be used as an argument to mysql_row_seek().

You should use mysql_row_tell() only after mysql_store_result(), not after mysql_use_result().

Return Values

The current offset of the row cursor.

Errors

None.

20.2.3.49 mysql_select_db()

int mysql_select_db(MYSQL *mysql, const char *db)

Description

Causes the database specified by db to become the default (current) database on the connection specified by mysql. In subsequent queries, this database is the default for table references that do not include an explicit database specifier.

mysql_select_db() fails unless the connected user can be authenticated as having permission to use the database.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.50 mysql_set_server_option()

int mysql_set_server_option(MYSQL *mysql, enum enum_mysql_set_option option)

Description

Enables or disables an option for the connection. option can have one of the following values:

MYSQL_OPTION_MULTI_STATEMENTS_ON Enable multi statement support.
MYSQL_OPTION_MULTI_STATEMENTS_OFF Disable multi statement support.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
ER_UNKNOWN_COM_ERROR
The server didn't support mysql_set_server_option() (which is the case that the server is older than 4.1.1) or the server didn't support the option one tried to set.

20.2.3.51 mysql_shutdown()

int mysql_shutdown(MYSQL *mysql)

Description

Asks the database server to shut down. The connected user must have SHUTDOWN privileges.

Return Values

Zero for success. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.52 mysql_sqlstate()

const char *mysql_sqlstate(MYSQL *mysql)

Description

Returns a null-terminated string containing the SQLSTATE error code for the last error. The error code consists of five characters. '00000' means ``no error''. The values are specified by ANSI SQL and ODBC. For a list of possible values, see section 21.1 Error Returns.

Note that not all MySQL errors are yet mapped to SQLSTATE's. The value 'HY000' (general error) is used for unmapped errors.

This function was added to MySQL 4.1.1.

Return Values

A null-terminated character string containing the SQLSTATE error code.

See Also

See section 20.2.3.12 mysql_errno(). See section 20.2.3.13 mysql_error(). See section 20.2.7.22 mysql_stmt_sqlstate().

20.2.3.53 mysql_ssl_set()

int mysql_ssl_set(MYSQL *mysql, const char *key, const char *cert, const char *ca, const char *capath, const char *cipher)

Description

mysql_ssl_set() is used for establishing secure connections using SSL. It must be called before mysql_real_connect().

mysql_ssl_set() does nothing unless OpenSSL support is enabled in the client library.

mysql is the connection handler returned from mysql_init(). The other parameters are specified as follows:

  • key is the pathname to the key file.
  • cert is the pathname to the certificate file.
  • ca is the pathname to the certificate authority file.
  • capath is the pathname to a directory that contains trusted SSL CA certificates in pem format.
  • cipher is a list of allowable ciphers to use for SSL encryption.

Any unused SSL parameters may be given as NULL.

Return Values

This function always returns 0. If SSL setup is incorrect, mysql_real_connect() will return an error when you attempt to connect.

20.2.3.54 mysql_stat()

char *mysql_stat(MYSQL *mysql)

Description

Returns a character string containing information similar to that provided by the mysqladmin status command. This includes uptime in seconds and the number of running threads, questions, reloads, and open tables.

Return Values

A character string describing the server status. NULL if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.55 mysql_store_result()

MYSQL_RES *mysql_store_result(MYSQL *mysql)

Description

You must call mysql_store_result() or mysql_use_result() for every query that successfully retrieves data (SELECT, SHOW, DESCRIBE, EXPLAIN).

You don't have to call mysql_store_result() or mysql_use_result() for other queries, but it will not do any harm or cause any notable performance if you call mysql_store_result() in all cases. You can detect if the query didn't have a result set by checking if mysql_store_result() returns 0 (more about this later one).

If you want to know if the query should return a result set or not, you can use mysql_field_count() to check for this. See section 20.2.3.20 mysql_field_count().

mysql_store_result() reads the entire result of a query to the client, allocates a MYSQL_RES structure, and places the result into this structure.

mysql_store_result() returns a null pointer if the query didn't return a result set (if the query was, for example, an INSERT statement).

mysql_store_result() also returns a null pointer if reading of the result set failed. You can check whether an error occurred by checking if mysql_error() returns a non-empty string, if mysql_errno() returns non-zero, or if mysql_field_count() returns zero.

An empty result set is returned if there are no rows returned. (An empty result set differs from a null pointer as a return value.)

Once you have called mysql_store_result() and got a result back that isn't a null pointer, you may call mysql_num_rows() to find out how many rows are in the result set.

You can call mysql_fetch_row() to fetch rows from the result set, or mysql_row_seek() and mysql_row_tell() to obtain or set the current row position within the result set.

You must call mysql_free_result() once you are done with the result set.

See section 20.2.12.1 Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success.

Return Values

A MYSQL_RES result structure with the results. NULL if an error occurred.

Errors

mysql_store_result() resets mysql_error and mysql_errno if it succeeds.

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_OUT_OF_MEMORY
Out of memory.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.56 mysql_thread_id()

unsigned long mysql_thread_id(MYSQL *mysql)

Description

Returns the thread ID of the current connection. This value can be used as an argument to mysql_kill() to kill the thread.

If the connection is lost and you reconnect with mysql_ping(), the thread ID will change. This means you should not get the thread ID and store it for later. You should get it when you need it.

Return Values

The thread ID of the current connection.

Errors

None.

20.2.3.57 mysql_use_result()

MYSQL_RES *mysql_use_result(MYSQL *mysql)

Description

You must call mysql_store_result() or mysql_use_result() for every query that successfully retrieves data (SELECT, SHOW, DESCRIBE, EXPLAIN).

mysql_use_result() initiates a result set retrieval but does not actually read the result set into the client like mysql_store_result() does. Instead, each row must be retrieved individually by making calls to mysql_fetch_row(). This reads the result of a query directly from the server without storing it in a temporary table or local buffer, which is somewhat faster and uses much less memory than mysql_store_result(). The client will allocate memory only for the current row and a communication buffer that may grow up to max_allowed_packet bytes.

On the other hand, you shouldn't use mysql_use_result() if you are doing a lot of processing for each row on the client side, or if the output is sent to a screen on which the user may type a ^S (stop scroll). This will tie up the server and prevent other threads from updating any tables from which the data is being fetched.

When using mysql_use_result(), you must execute mysql_fetch_row() until a NULL value is returned, otherwise, the unfetched rows will be returned as part of the result set for your next query. The C API will give the error Commands out of sync; you can't run this command now if you forget to do this!

You may not use mysql_data_seek(), mysql_row_seek(), mysql_row_tell(), mysql_num_rows(), or mysql_affected_rows() with a result returned from mysql_use_result(), nor may you issue other queries until the mysql_use_result() has finished. (However, after you have fetched all the rows, mysql_num_rows() will accurately return the number of rows fetched.)

You must call mysql_free_result() once you are done with the result set.

Return Values

A MYSQL_RES result structure. NULL if an error occurred.

Errors

mysql_use_result() resets mysql_error and mysql_errno if it succeeds.

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_OUT_OF_MEMORY
Out of memory.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.3.58 mysql_warning_count()

unsigned int mysql_warning_count(MYSQL *mysql)

Description

Returns the number of warnings generated during execution of the previous SQL statement. Available from MySQL 4.1.

Return Values

The warning count.

Errors

None.

20.2.3.59 mysql_commit()

my_bool mysql_commit(MYSQL *mysql)

Description

Commits the current transaction. Available from MySQL 4.1.

Return Values

Zero if successful. Non-zero if an error occurred.

Errors

None.

20.2.3.60 mysql_rollback()

my_bool mysql_rollback(MYSQL *mysql)

Description

Rolls back the current transaction. Available from MySQL 4.1.

Return Values

Zero if successful. Non-zero if an error occurred.

Errors

None.

20.2.3.61 mysql_autocommit()

my_bool mysql_autocommit(MYSQL *mysql, my_bool mode)

Description

Sets autocommit mode on if mode is 1, off if mode is 0. Available from MySQL 4.1.

Return Values

Zero if successful. Non-zero if an error occurred.

Errors

None.

20.2.3.62 mysql_more_results()

my_bool mysql_more_results(MYSQL *mysql)

Description

Returns true if more results exist from the currently executed query, and the application must call mysql_next_result() to fetch the results. Available from MySQL 4.1.

Return Values

TRUE (1) if more results exist. FALSE (0) if no more results exist.

Note that in most cases one instead call mysql_next_result() to test whether more results exist and initiate the next result set if it existed.

See section 20.2.8 C API Handling of Multiple Query Execution. See section 20.2.3.63 mysql_next_result().

Errors

None.

20.2.3.63 mysql_next_result()

int mysql_next_result(MYSQL *mysql)

Description

If more query results exist, mysql_next_result() reads the next query results and returns the status back to application. Available from MySQL 4.1.

Note that you must call mysql_free_result() for the preceding query if it returned a result set.

After calling mysql_next_result() the state of the connection is as if you had called mysql_real_query() for the next query. This means that you can now call mysql_store_result(), mysql_warning_count(), mysql_affected_rows() ... on the connection.

If mysql_next_result() returns an error, no other statements will be executed and there is no more results to fetch.

See section 20.2.8 C API Handling of Multiple Query Execution.

Return Values

0 if successful and there was more results -1 if no more results > 0 if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order. For example if you didn't call mysql_use_result() for a previous result set.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.4 C API Prepared Statements

As of MySQL 4.1, the client/server protocol provides for the use of prepared statements. This capability uses the MYSQL_STMT statement handler data structure. Prepared execution is an efficient way to execute a statement more than once. The statement is first parsed to prepare it for execution. Then it is executed one or more times at a later time, using the statement handle returned by the prepare function.

Prepared execution is faster than direct execution for statements executed more than once, primarly because the query is parsed only once. In the case of direct execution, the query is parsed every time it is executed. Prepared execution also can provide a reduction of network traffic because for each execution of the prepared statement, it is necessary only to send the data for the parameters.

Another advantage of prepared statements is that it uses a binary protocol that makes data transfer between client and server more efficient. Prepared statements also can support input and output binding for multiple query execution.

20.2.5 C API Prepared Statement Datatypes

Note: The API for prepared statements is still subject to revision. This information is provided for early adopters, but please be aware that the API may change. Some incompatible changes were made in MySQL 4.1.2. See section 20.2.7 C API Prepared Statement Function Descriptions for details.

Prepared statements mainly use the MYSQL_STMT and MYSQL_BIND data structures. A third structure, MYSQL_TIME, is used to transfer temporal data.

MYSQL_STMT
This structure represents a prepared statement. A statement is created by calling mysql_stmt_init(), which returns a statement handle, that is, a pointer to a MYSQL_STMT. The handle is used for all subsequent statement-related functions. The MYSQL_STMT structure has no members that are for application use. Multiple statement handles can be associated with a single connection. The limit on the number of handles depends on the available system resources.
MYSQL_BIND
This structure is used both for query input (data values sent to the server) and output (result values returned from the server). For input, it is used with mysql_stmt_bind_param() to bind parameter data values to buffers for use by mysql_stmt_execute(). For output, it is used with mysql_stmt_bind_result() to bind result set buffers for use in fetching rows with mysql_stmt_fetch(). The MYSQL_BIND structure contains the following members for use by application programs. Each is used both for input and for output, though sometimes for different purposes depending on the direction of data transfer.
enum enum_field_types buffer_type
The type of the buffer. The allowable buffer_type values are listed later in this section. For input, buffer_type indicates what type of value you are binding to a query parameter. For output, it indicates what type of value you expect to receive in a result buffer.
void *buffer
For input, this is a pointer to the buffer in which a query parameter's data value is stored. For output, it is a pointer to the buffer in which to return a result set column value. For numeric column types, buffer should point to a variable of the proper C type. (If you are associating the variable with a column that has the UNSIGNED attribute, the variable should be an unsigned C type.) For date and time column types, buffer should point to a MYSQL_TIME structure. For character and binary string column types, buffer should point to a character buffer.
unsigned long buffer_length
The actual size of *buffer in bytes. This indicates the maximum amount of data that can be stored in the buffer. For character and binary C data, the buffer_length value specifies the length of *buffer when used with mysql_stmt_bind_param(), or the maximum number of data bytes that can be fetched into the buffer when used with mysql_stmt_bind_result().
unsigned long *length
A pointer to an unsigned long variable that indicates the actual number of bytes of data stored in *buffer. length is used for character or binary C data. For input parameter data binding, length points to an unsigned long variable that indicates the length of the parameter value stored in *buffer; this is used by mysql_stmt_execute(). If length is a null pointer, the protocol assumes that all character and binary data are null-terminated. For output value binding, mysql_stmt_fetch() places the length of the column value that is returned into the variable that length points to. length is ignored for numeric and temporal datatypes because the length of the data value is determined by the buffer_type value.
my_bool *is_null
This member points to a my_bool variable that is true if a value is NULL, false if it is not NULL. For input, set *is_null to true to indicate that you are passing a NULL value as a query parameter. For output, this value will be set to true after you fetch a row if the result value returned from the query is NULL.
MYSQL_TIME
This structure is used to send and receive DATE, TIME, DATETIME, and TIMESTAMP data directly to and from the server. This is done by setting the buffer_type member of a MYSQL_BIND structure to one of the temporal types, and setting the buffer member to point to a MYSQL_TIME structure. The MYSQL_TIME structure contains the following members:
unsigned int year
The year.
unsigned int month
The month of the year.
unsigned int day
The day of the month.
unsigned int hour
The hour of the day.
unsigned int minute
The minute of the hour.
unsigned int second
The second of the minute.
my_bool neg
A boolean flag to indicate whether the time is negative.
unsigned long second_part
The fractional part of the second. This member currently is unused.
Only those parts of a MYSQL_TIME structure that apply to a given type of temporal value are used: The year, month, and day elements are used for DATE, DATETIME, and TIMESTAMP values. The hour, minute, and second elements are used for TIME, DATETIME, and TIMESTAMP values. See section 20.2.9 C API Handling of Date and Time Values.

The following table shows the allowable values that may be specified in the buffer_type member of MYSQL_BIND structures. The table also shows those SQL types that correspond most closely to each buffer_type value, and, for numeric and temporal types, the corresponding C type.

buffer_type Value SQL Type C Type
MYSQL_TYPE_TINY TINYINT char
MYSQL_TYPE_SHORT SMALLINT short int
MYSQL_TYPE_LONG INT long int
MYSQL_TYPE_LONGLONG BIGINT long long int
MYSQL_TYPE_FLOAT FLOAT float
MYSQL_TYPE_DOUBLE DOUBLE double
MYSQL_TYPE_TIME TIME MYSQL_TIME
MYSQL_TYPE_DATE DATE MYSQL_TIME
MYSQL_TYPE_DATETIME DATETIME MYSQL_TIME
MYSQL_TYPE_TIMESTAMP TIMESTAMP MYSQL_TIME
MYSQL_TYPE_STRING CHAR
MYSQL_TYPE_VAR_STRING VARCHAR
MYSQL_TYPE_TINY_BLOB TINYBLOB/TINYTEXT
MYSQL_TYPE_BLOB BLOB/TEXT
MYSQL_TYPE_MEDIUM_BLOB MEDIUMBLOB/MEDIUMTEXT
MYSQL_TYPE_LONG_BLOB LONGBLOB/LONGTEXT

Implicit type conversion may be performed in both directions.

20.2.6 C API Prepared Statement Function Overview

Note: The API for prepared statements is still subject to revision. This information is provided for early adopters, but please be aware that the API may change. Some incompatible changes were made in MySQL 4.1.2. See section 20.2.7 C API Prepared Statement Function Descriptions for details.

The functions available for prepared statement processing are summarized here and described in greater detail in a later section. See section 20.2.7 C API Prepared Statement Function Descriptions.

Function Description
mysql_stmt_init() Allocates memory for MYSQL_STMT structure and initializes it.
mysql_stmt_bind_param() Associates application data buffers with the parameter markers in a prepared SQL statement.
mysql_stmt_bind_result() Associates application data buffers with columns in the result set.
mysql_stmt_execute() Executes the prepared statement.
mysql_stmt_fetch() Fetches the next row of data from the result set and returns data for all bound columns.
mysql_stmt_fetch_column() Fetch data for one column of the current row of the result set.
mysql_stmt_result_metadata() Returns prepared statement metadata in the form of a result set.
mysql_stmt_param_count() Returns the number of parameters in a prepared SQL statement.
mysql_stmt_param_metadata() Return parameter metadata in the form of a result set.
mysql_stmt_prepare() Prepares an SQL string for execution.
mysql_stmt_send_long_data() Sends long data in chunks to server.
mysql_stmt_affected_rows() Returns the number of rows changes, deleted, or inserted by the last UPDATE, DELETE, or INSERT query.
mysql_stmt_close() Frees memory used by prepared statement.
mysql_stmt_data_seek() Seeks to an arbitrary row number in a statement result set.
mysql_stmt_errno() Returns the error number for the last statement execution.
mysql_stmt_error() Returns the error message for the last statement execution.
mysql_stmt_free_result() Free the resources allocated to the statement handle.
mysql_stmt_num_rows() Returns total rows from the statement buffered result set.
mysql_stmt_reset() Reset the statement buffers in the server.
mysql_stmt_row_seek() Seeks to a row offset in a statement result set, using value returned from mysql_stmt_row_tell().
mysql_stmt_row_tell() Returns the statement row cursor position.
mysql_stmt_sqlstate() Returns the SQLSTATE error code for the last statement execution.
mysql_stmt_store_result() Retrieves the complete result set to the client.

Call mysql_stmt_init() to create a statement handle, then mysql_stmt_prepare to prepare it, mysql_stmt_bind_param() to supply the parameter data, and mysql_stmt_execute() to execute the query. You can repeat the mysql_stmt_execute() by changing parameter values in the respective buffers supplied through mysql_stmt_bind_param().

If the query is a SELECT statement or any other query that produces a result set, mysql_stmt_prepare() will also return the result set metadata information in the form of a MYSQL_RES result set through mysql_stmt_result_metadata().

You can supply the result buffers using mysql_stmt_bind_result(), so that the mysql_stmt_fetch() will automatically return data to these buffers. This is row-by-row fetching.

You can also send the text or binary data in chunks to server using mysql_stmt_send_long_data(), by specifying the option is_long_data=1 or length=MYSQL_LONG_DATA or -2 in the MYSQL_BIND structure supplied with mysql_stmt_bind_param().

When statement execution has been completed, the statement handle must be closed using mysql_stmt_close() so that all resources associated with it can be freed.

If you obtained a SELECT statement's result set metadata by calling mysql_stmt_result_metadata(), you should also free it using mysql_stmt_free_result().

Execution Steps

To prepare and execute a statement, an application follows these steps:

  1. Create a prepared statement handle with msyql_stmt_init(). Call mysql_stmt_prepare() and pass it a string containing the SQL statement to prepare the statement on the server.
  2. If the query produces a result set, call mysql_stmt_result_metadata() to obtain the result set metadata. This metadata is itself in the form of result set, albeit a separate one from the one that contains the rows returned by the query. The metadata result set indicates how many columns are in the result and contains information about each column.
  3. Set the values of any parameters using mysql_stmt_bind_param(). All parameters must be set. Otherwise, query execution will return an error or produce unexpected results.
  4. Call mysql_stmt_execute() to execute the statement.
  5. If the query produces a result set, bind the data buffers to use for retrieving the row values by calling mysql_stmt_bind_result().
  6. Fetch the data into the buffers row by row by calling mysql_stmt_fetch() repeatedly until no more rows are found.
  7. Repeat steps 3 through 6 as necessary, by changing the parameter values and re-executing the statement.

When mysql_stmt_prepare() is called, the MySQL client/server protocol performs these actions:

  • The server parses the query and sends the okay status back to the client by assigning a statement ID. It also sends total number of parameters, a column count, and its meta information if it is a result set oriented query. All syntax and semantics of the query are checked by the server during this call.
  • The client uses this statement ID for the further operations, so that the server can identify the statement from among its pool of statements.

When mysql_stmt_execute() is called, the MySQL client/server protocol performs these actions:

  • The client uses the statement handle and sends the parameter data to the server.
  • The server identifies the statement using the ID provided by the client, replaces the parameter markers with the newly supplied data, and executes the query. If the query produces a result set, the server sends the data back to the client. Otherwise, it sends an okay status and total number of rows changed, deleted, or inserted.

When mysql_stmt_fetch() is called, the MySQL client/server protocol performs these actions:

  • The client reads the data from the packet row by row and places it into the application data buffers by doing the necessary conversions. If the application buffer type is same as that of the field type returned from the server, the conversions are straightforward.

You can get the statement error code, error message, and SQLSTATE value using mysql_stmt_errno(), mysql_stmt_error(), and mysql_stmt_sqlstate(), respectively.

20.2.7 C API Prepared Statement Function Descriptions

To prepare and execute queries, use the functions in the following sections.

Note: The API for prepared statements is still subject to revision. This information is provided for early adopters, but please be aware that the API may change.

In MySQL 4.1.2, the names of several prepared statement functions were changed:

Old Name New Name
mysql_bind_param() mysql_stmt_bind_param()
mysql_bind_result() mysql_stmt_bind_result()
mysql_prepare() mysql_stmt_prepare()
mysql_execute() mysql_stmt_execute()
mysql_fetch() mysql_stmt_fetch()
mysql_fetch_column() mysql_stmt_fetch_column()
mysql_param_count() mysql_stmt_param_count()
mysql_param_result() mysql_stmt_param_metadata()
mysql_get_metadata() mysql_stmt_result_metadata()
mysql_send_long_data() mysql_stmt_send_long_data()

Now all functions that operate with a MYSQL_STMT structure begin with the prefix mysql_stmt_.

Also in 4.1.2, the signature of the mysql_stmt_prepare() function was changed to int mysql_stmt_prepare(MYSQL_STMT *stmt, const char *query, unsigned long length). To create a MYSQL_STMT handle, you should use the mysql_stmt_init() function.

20.2.7.1 mysql_stmt_init()

MYSQL_STMT *mysql_stmt_init(MYSQL *mysql)

Description

Create a MYSQL_STMT handle.

Return values

A pointer to a MYSQL_STMT structure in case of success. NULL if out of memory.

Errors

CR_OUT_OF_MEMORY
Out of memory.

20.2.7.2 mysql_stmt_bind_param()

my_bool mysql_stmt_bind_param(MYSQL_STMT *stmt, MYSQL_BIND *bind)

Description

mysql_stmt_bind_param() is used to bind data for the parameter markers in the SQL statement that was passed to mysql_stmt_prepare(). It uses MYSQL_BIND structures to supply the data. bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain an element for each `?' parameter marker that is present in the query.

Suppose you prepare the following statment:

INSERT INTO mytbl VALUES(?,?,?)

When you bind the parameters, the array of MYSQL_BIND structures must contain three elements, and can be declared like this:

MYSQL_BIND bind[3];

The members of each MYSQL_BIND element that should be set are described in section 20.2.5 C API Prepared Statement Datatypes.

Return Values

Zero if the bind was successful. Non-zero if an error occurred.

Errors

CR_INVALID_BUFFER_USE
Indicates if the bind is to supply the long data in chunks and if the buffer type is non string or binary.
CR_UNSUPPORTED_PARAM_TYPE
The conversion is not supported. Possibly the buffer_type value is illegal or is not one of the supported types.
CR_OUT_OF_MEMORY
Out of memory.
CR_UNKNOWN_ERROR
An unknown error occurred.

Example

For the usage of mysql_stmt_bind_param(), refer to the Example from section 20.2.7.4 mysql_stmt_execute().

20.2.7.3 mysql_stmt_bind_result()

my_bool mysql_stmt_bind_result(MYSQL_STMT *stmt, MYSQL_BIND *bind)

Description

mysql_stmt_bind_result() is used to associate (bind) columns in the result set to data buffers and length buffers. When mysql_stmt_fetch() is called to fetch data, the MySQL client/server protocol places the data for the bound columns into the specified buffers.

Note that all columns must be bound to buffers prior to calling mysql_stmt_fetch(). bind is the address of an array of MYSQL_BIND structures. The client library expects the array to contain an element for each column of the result set. Otherwise, mysql_stmt_fetch() simply ignores the data fetch. Also, the buffers should be large enough to hold the data values, because the protocol doesn't return data values in chunks.

A column can be bound or rebound at any time, even after a result set has been partially retrieved. The new binding takes effect the next time mysql_stmt_fetch() is called. Suppose an application binds the columns in a result set and calls mysql_stmt_fetch(). The client/server protocol returns data in the bound buffers. Then suppose the application binds the columns to a different set of buffers. The protocol does not place data into the newly bound buffers until the next call to mysql_stmt_fetch() occurs.

To bind a column, an application calls mysql_stmt_bind_result() and passes the type, address, and the address of the length buffer. The members of each MYSQL_BIND element that should be set are described in section 20.2.5 C API Prepared Statement Datatypes.

Return Values

Zero if the bind was successful. Non-zero if an error occurred.

Errors

CR_UNSUPPORTED_PARAM_TYPE
The conversion is not supported. Possibly the buffer_type value is illegal or is not one of the supported types.
CR_OUT_OF_MEMORY
Out of memory.
CR_UNKNOWN_ERROR
An unknown error occurred.

Example

For the usage of mysql_stmt_bind_result(), refer to the Example from section 20.2.7.5 mysql_stmt_fetch().

20.2.7.4 mysql_stmt_execute()

int mysql_stmt_execute(MYSQL_STMT *stmt)

Description

mysql_stmt_execute() executes the prepared query associated with the statement handle. The currently bound parameter marker values are sent to server during this call, and the server replaces the markers with this newly supplied data.

If the statement is an UPDATE, DELETE, or INSERT, the total number of changed, deleted, or inserted rows can be found by calling mysql_stmt_affected_rows(). If this is a result set query such as SELECT, you must call mysql_stmt_fetch() to fetch the data prior to calling any other functions that result in query processing. For more information on how to fetch the results, refer to section 20.2.7.5 mysql_stmt_fetch().

Return Values

Zero if execution was successful. Non-zero if an error occurred. The error code and message can be obtained by calling mysql_stmt_errno() and mysql_stmt_error().

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_OUT_OF_MEMORY
Out of memory.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

Example

The following example demonstrates how to create and populate a table using mysql_stmt_prepare(), mysql_stmt_param_count(), mysql_stmt_bind_param(), mysql_stmt_execute(), and mysql_stmt_affected_rows(). The mysql variable is assumed to be a valid connection handle.

#define STRING_SIZE 50

#define DROP_SAMPLE_TABLE "DROP TABLE IF EXISTS test_table"
#define CREATE_SAMPLE_TABLE "CREATE TABLE test_table(col1 INT,\
                                                 col2 VARCHAR(40),\
                                                 col3 SMALLINT,\
                                                 col4 TIMESTAMP)"
#define INSERT_SAMPLE "INSERT INTO test_table(col1,col2,col3) VALUES(?,?,?)"

MYSQL_STMT    *stmt;
MYSQL_BIND    bind[3];
my_ulonglong  affected_rows;
int           param_count;
short         small_data;
int           int_data;
char          str_data[STRING_SIZE];
unsigned long str_length;
my_bool       is_null;

if (mysql_query(mysql, DROP_SAMPLE_TABLE))
{
  fprintf(stderr, " DROP TABLE failed\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}

if (mysql_query(mysql, CREATE_SAMPLE_TABLE))
{
  fprintf(stderr, " CREATE TABLE failed\n");
  fprintf(stderr, " %s\n", mysql_error(mysql));
  exit(0);
}

/* Prepare an INSERT query with 3 parameters */
/* (the TIMESTAMP column is not named; it will */
/* be set to the current date and time) */
stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(mysql, INSERT_SAMPLE, strlen(INSERT_SAMPLE)))
{
  fprintf(stderr, " mysql_stmt_prepare(), INSERT failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
fprintf(stdout, " prepare, INSERT successful\n");

/* Get the parameter count from the statement */
param_count= mysql_stmt_param_count(stmt);
fprintf(stdout, " total parameters in INSERT: %d\n", param_count);

if (param_count != 3) /* validate parameter count */
{
  fprintf(stderr, " invalid parameter count returned by MySQL\n");
  exit(0);
}

/* Bind the data for all 3 parameters */

/* INTEGER PARAM */
/* This is a number type, so there is no need to specify buffer_length */
bind[0].buffer_type= MYSQL_TYPE_LONG;
bind[0].buffer= (char *)&int_data;
bind[0].is_null= 0;
bind[0].length= 0;

/* STRING PARAM */
bind[1].buffer_type= MYSQL_TYPE_VAR_STRING;
bind[1].buffer= (char *)str_data;
bind[1].buffer_length= STRING_SIZE;
bind[1].is_null= 0;
bind[1].length= &str_length;
 
/* SMALLINT PARAM */
bind[2].buffer_type= MYSQL_TYPE_SHORT;
bind[2].buffer= (char *)&small_data;       
bind[2].is_null= &is_null;
bind[2].length= 0;

/* Bind the buffers */
if (mysql_stmt_bind_param(stmt, bind))
{
  fprintf(stderr, " mysql_stmt_bind_param() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Specify the data values for the first row */
int_data= 10;             /* integer */
strncpy(str_data, "MySQL", STRING_SIZE); /* string  */
str_length= strlen(str_data);

/* INSERT SMALLINT data as NULL */
is_null= 1;

/* Execute the INSERT statement - 1*/
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute(), 1 failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
  
/* Get the total number of affected rows */   
affected_rows= mysql_stmt_affected_rows(stmt);
fprintf(stdout, " total affected rows(insert 1): %ld\n", affected_rows);

if (affected_rows != 1) /* validate affected rows */
{
  fprintf(stderr, " invalid affected rows by MySQL\n");
  exit(0);
}

/* Specify data values for second row, then re-execute the statement */
int_data= 1000;             
strncpy(str_data, "The most popular open source database", STRING_SIZE); 
str_length= strlen(str_data);
small_data= 1000;         /* smallint */
is_null= 0;               /* reset */

/* Execute the INSERT statement - 2*/
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute, 2 failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
  
/* Get the total rows affected */   
affected_rows= mysql_stmt_affected_rows(stmt);
fprintf(stdout, " total affected rows(insert 2): %ld\n", affected_rows);

if (affected_rows != 1) /* validate affected rows */
{
  fprintf(stderr, " invalid affected rows by MySQL\n");
  exit(0);
}

/* Close the statement */
if (mysql_stmt_close(stmt))
{
  fprintf(stderr, " failed while closing the statement\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

Note: For complete examples on the use of prepared statement functions, refer to the file `tests/client_test.c'. This file can be obtained from a MySQL source distribution or from the BitKeeper source repository.

20.2.7.5 mysql_stmt_fetch()

int mysql_stmt_fetch(MYSQL_STMT *stmt)

Description

mysql_stmt_fetch() returns the next row in the result set. It can be called only while the result set exists, that is, after a call to mysql_stmt_execute() that creates a result set or after mysql_stmt_store_result(), which is called after mysql_stmt_execute() to buffer the entire result set.

mysql_stmt_fetch() returns row data using the buffers bound by mysql_stmt_bind_result(). It returns the data in those buffers for all the columns in the current row set and the lengths are returned to the length pointer.

Note that all columns must be bound by the application before calling mysql_stmt_fetch().

If a fetched data value is a NULL value, the *is_null value of the corresponding MYSQL_BIND structure contains TRUE (1). Otherwise, the data and its length are returned in the *buffer and *length elements based on the buffer type specified by the application. Each numeric and temporal type has a fixed length, as listed in the following table. The length of the string types depends on the length of the actual data value, as indicated by data_length.

Type Length
MYSQL_TYPE_TINY 1
MYSQL_TYPE_SHORT 2
MYSQL_TYPE_LONG 4
MYSQL_TYPE_LONGLONG 8
MYSQL_TYPE_FLOAT 4
MYSQL_TYPE_DOUBLE 8
MYSQL_TYPE_TIME sizeof(MYSQL_TIME)
MYSQL_TYPE_DATE sizeof(MYSQL_TIME)
MYSQL_TYPE_DATETIME sizeof(MYSQL_TIME)
MYSQL_TYPE_TIMESTAMP sizeof(MYSQL_TIME)
MYSQL_TYPE_STRING data length
MYSQL_TYPE_VAR_STRING data_length
MYSQL_TYPE_TINY_BLOB data_length
MYSQL_TYPE_BLOB data_length
MYSQL_TYPE_MEDIUM_BLOB data_length
MYSQL_TYPE_LONG_BLOB data_length

Return Values

Return Value Description
0 Successful, the data has been fetched to application data buffers.
1 Error occurred. Error code and message can be obtained by calling mysql_stmt_errno() and mysql_stmt_error().
MYSQL_NO_DATA No more rows/data exists

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_OUT_OF_MEMORY
Out of memory.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.
CR_UNSUPPORTED_PARAM_TYPE
The buffer type is MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, or MYSQL_TYPE_TIMESTAMP, but the datatype is not DATE, TIME, DATETIME, or TIMESTAMP.
All other unsupported conversion errors are returned from mysql_stmt_bind_result().

Example

The following example demonstrates how to fetch data from a table using mysql_stmt_result_metadata(), mysql_stmt_bind_result(), and mysql_stmt_fetch(). (This example expects to retrieve the two rows inserted by the example shown in section 20.2.7.4 mysql_stmt_execute().) The mysql variable is assumed to be a valid connection handle.

#define STRING_SIZE 50

#define SELECT_SAMPLE "SELECT col1, col2, col3, col4 FROM test_table"

MYSQL_STMT    *stmt;
MYSQL_BIND    bind[4];
MYSQL_RES     *prepare_meta_result;
MYSQL_TIME    ts;
unsigned long length[4];
int           param_count, column_count, row_count;
short         small_data;
int           int_data;
char          str_data[STRING_SIZE];
my_bool       is_null[4];

/* Prepare a SELECT query to fetch data from test_table */
stmt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, SELECT_SAMPLE, strlen(SELECT_SAMPLE)))
{
  fprintf(stderr, " mysql_stmt_prepare(), SELECT failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}
fprintf(stdout, " prepare, SELECT successful\n");

/* Get the parameter count from the statement */
param_count= mysql_stmt_param_count(stmt);
fprintf(stdout, " total parameters in SELECT: %d\n", param_count);

if (param_count != 0) /* validate parameter count */
{
  fprintf(stderr, " invalid parameter count returned by MySQL\n");
  exit(0);
}

/* Fetch result set meta information */
prepare_meta_result = mysql_stmt_result_metadata(stmt);
if (!prepare_meta_result)
{
  fprintf(stderr,
         " mysql_stmt_result_metadata(), returned no meta information\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Get total columns in the query */
column_count= mysql_num_fields(prepare_meta_result);
fprintf(stdout, " total columns in SELECT statement: %d\n", column_count);

if (column_count != 4) /* validate column count */
{
  fprintf(stderr, " invalid column count returned by MySQL\n");
  exit(0);
}

/* Execute the SELECT query */
if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, " mysql_stmt_execute(), failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Bind the result buffers for all 4 columns before fetching them */

/* INTEGER COLUMN */
bind[0].buffer_type= MYSQL_TYPE_LONG;
bind[0].buffer= (char *)&int_data;
bind[0].is_null= &is_null[0];
bind[0].length= &length[0];

/* STRING COLUMN */
bind[1].buffer_type= MYSQL_TYPE_VAR_STRING;
bind[1].buffer= (char *)str_data;
bind[1].buffer_length= STRING_SIZE;
bind[1].is_null= &is_null[1];
bind[1].length= &length[1];
 
/* SMALLINT COLUMN */
bind[2].buffer_type= MYSQL_TYPE_SHORT;
bind[2].buffer= (char *)&small_data;       
bind[2].is_null= &is_null[2];
bind[2].length= &length[2];
 
/* TIMESTAMP COLUMN */
bind[3].buffer_type= MYSQL_TYPE_TIMESTAMP;
bind[3].buffer= (char *)&ts;       
bind[3].is_null= &is_null[3];
bind[3].length= &length[3];

/* Bind the result buffers */
if (mysql_stmt_bind_result(stmt, bind))
{
  fprintf(stderr, " mysql_stmt_bind_result() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Now buffer all results to client */
if (mysql_stmt_store_result(stmt))
{
  fprintf(stderr, " mysql_stmt_store_result() failed\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

/* Fetch all rows */
row_count= 0;
fprintf(stdout, "Fetching results ...\n");
while (!mysql_stmt_fetch(stmt))
{
  row_count++;
  fprintf(stdout, "  row %d\n", row_count);

  /* column 1 */
  fprintf(stdout, "   column1 (integer)  : ");
  if (is_null[0])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %d(%ld)\n", int_data, length[0]);

  /* column 2 */
  fprintf(stdout, "   column2 (string)   : ");
  if (is_null[1])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %s(%ld)\n", str_data, length[1]);

  /* column 3 */
  fprintf(stdout, "   column3 (smallint) : ");
  if (is_null[2])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %d(%ld)\n", small_data, length[2]);

  /* column 4 */
  fprintf(stdout, "   column4 (timestamp): ");
  if (is_null[3])
    fprintf(stdout, " NULL\n");
  else
    fprintf(stdout, " %04d-%02d-%02d %02d:%02d:%02d (%ld)\n",
                                               ts.year, ts.month, ts.day,
                                               ts.hour, ts.minute, ts.second,
                                               length[3]);
  fprintf(stdout, "\n");
}

/* Validate rows fetched */
fprintf(stdout, " total rows fetched: %d\n", row_count);
if (row_count != 2)
{
  fprintf(stderr, " MySQL failed to return all rows\n");
  exit(0);
} 

/* Free the prepared result metadata */
mysql_free_result(prepare_meta_result);

/* Close the statement */
if (mysql_stmt_close(stmt))
{
  fprintf(stderr, " failed while closing the statement\n");
  fprintf(stderr, " %s\n", mysql_stmt_error(stmt));
  exit(0);
}

20.2.7.6 mysql_stmt_fetch_column()

int mysql_stmt_fetch_column(MYSQL_STMT *stmt, MYSQL_BIND *bind, unsigned int column, unsigned long offset)

Description

Return Values

Errors

20.2.7.7 mysql_stmt_result_metadata()

MYSQL_RES *mysql_stmt_result_metadata(MYSQL_STMT *stmt)

Description

If a statement passed to mysql_stmt_prepare() is one that produces a result set, mysql_stmt_rseult_metadata() returns the result set metadata in the form of a pointer to a MYSQL_RES structure that can be used to process the meta information such as total number of fields and individual field information. This result set pointer can be passed as an argument to any of the field-based API functions that process result set metadata, such as:

  • mysql_num_fields()
  • mysql_fetch_field()
  • mysql_fetch_field_direct()
  • mysql_fetch_fields()
  • mysql_field_count()
  • mysql_field_seek()
  • mysql_field_tell()
  • mysql_free_result()

The result set structure should be freed when you are done with it, which you can do by passing it to mysql_free_result(). This is similar to the way you free a result set obtained from a call to mysql_store_result().

The result set returned by mysql_stmt_result_metadata() contains only metadata. It does not contain any row results. The rows are obtained by using the statement handle with mysql_stmt_fetch().

Return Values

A MYSQL_RES result structure. NULL if no meta information exists for the prepared query.

Errors

CR_OUT_OF_MEMORY
Out of memory.
CR_UNKNOWN_ERROR
An unknown error occurred.

Example

For the usage of mysql_stmt_result_metadata(), refer to the Example from section 20.2.7.5 mysql_stmt_fetch().

20.2.7.8 mysql_stmt_param_count()

unsigned long mysql_stmt_param_count(MYSQL_STMT *stmt)

Description

Returns the number of parameter markers present in the prepared statement.

Return Values

An unsigned long integer representing the number of parameters in a statement.

Errors

None.

Example

For the usage of mysql_stmt_param_count(), refer to the Example from section 20.2.7.4 mysql_stmt_execute().

20.2.7.9 mysql_stmt_param_metadata()

MYSQL_RES *mysql_stmt_param_metadata(MYSQL_STMT *stmt)

To be added.

Description

Return Values

Errors

20.2.7.10 mysql_stmt_prepare()

int mysql_stmt_prepare(MYSQL_STMT *stmt, const char *query, unsigned long length)

Description

Prepares the SQL query pointed to by the null-terminated string query, and returns a statement handle to be used for further operations on the statement. The query must consist of a single SQL statement. You should not add a terminating semicolon (`;') or \g to the statement.

The application can include one or more parameter markers in the SQL statement by embedding question mark (`?') characters into the SQL string at the appropriate positions.

The markers are legal only in certain places in SQL statements. For example, they are allowed in the VALUES() list of an INSERT statement (to specify column values for a row), or in a comparison with a column in a WHERE clause to specify a comparison value. However, they are not allowed for identifiers (such as table or column names), in the select list that names the columns to be returned by a SELECT statement), or to specify both operands of a binary operator such as the = equal sign. The latter restriction is necessary because it would be impossible to determine the parameter type. In general, parameters are legal only in Data Manipulation Languange (DML) statements, and not in Data Defination Language (DDL) statements.

The parameter markers must be bound to application variables using mysql_stmt_bind_param() before executing the statement.

Return Values

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_OUT_OF_MEMORY
Out of memory.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query
CR_UNKNOWN_ERROR
An unknown error occurred.

If the prepare is not successful (that is, mysql_stmt_prepare() returns NULL), the error message can be obtained by calling mysql_error().

Example

For the usage of mysql_stmt_prepare(), refer to the Example from section 20.2.7.4 mysql_stmt_execute().

20.2.7.11 mysql_stmt_send_long_data()

my_bool mysql_stmt_send_long_data(MYSQL_STMT *stmt, unsigned int parameter_number, const char *data, unsigned long length)

Description

Allows an application to send parameter data to the server in pieces (or ``chunks''). This function can be called multiple times to send the parts of a character or binary data value for a column, which must be one of the TEXT or BLOB datatypes.

parameter_number indicates which parameter to associate the data with. Parameters are numbered beginning with 0. data is a pointer to a buffer containing data to be sent, and length indicates the number of bytes in the buffer.

Return Values

Zero if the data is sent successfully to server. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_OUT_OF_MEMORY
Out of memory.
CR_UNKNOWN_ERROR
An unknown error occurred.

Example

The following example demonstrates how to send the data for a TEXT column in chunks. It inserts the data value 'MySQL - The most popular open source database' into the text_column column. The mysql variable is assumed to be a valid connection handle.

#define INSERT_QUERY "INSERT INTO test_long_data(text_column) VALUES(?)"
  
MYSQL_BIND bind[1];
long       length;

smtt = mysql_stmt_init(mysql);
if (!stmt)
{
  fprintf(stderr, " mysql_stmt_init(), out of memory\n");
  exit(0);
}
if (mysql_stmt_prepare(stmt, INSERT_QUERY, strlen(INSERT_QUERY)))
{
  fprintf(stderr, "\n mysql_stmt_prepare(), INSERT failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}
 memset(bind, 0, sizeof(bind));
 bind[0].buffer_type= MYSQL_TYPE_STRING;
 bind[0].length= &length;
 bind[0].is_null= 0;

/* Bind the buffers */
if (mysql_stmt_bind_param(stmt, bind))
{
  fprintf(stderr, "\n param bind failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Supply data in chunks to server */
 if (!mysql_stmt_send_long_data(stmt,0,"MySQL",5))
{
  fprintf(stderr, "\n send_long_data failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Supply the next piece of data */
 if (mysql_stmt_send_long_data(stmt,0," - The most popular open source database",40))
{
  fprintf(stderr, "\n send_long_data failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

 /* Now, execute the query */
 if (mysql_stmt_execute(stmt))
{
  fprintf(stderr, "\n mysql_stmt_execute failed");
  fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
  exit(0);
}

20.2.7.12 mysql_stmt_affected_rows()

my_ulonglong mysql_stmt_affected_rows(MYSQL_STMT *stmt)

Description

Returns the total number of rows changed, deleted, or inserted by the last executed statement. May be called immediatlely after mysql_stmt_execute() for UPDATE, DELETE, or INSERT statements. For SELECT statements, mysql_stmt_affected_rows() works like mysql_num_rows().

Return Values

An integer greater than zero indicates the number of rows affected or retrieved. Zero indicates that no records were updated for an UPDATE statement, no rows matched the WHERE clause in the query, or that no query has yet been executed. -1 indicates that the query returned an error or that, for a SELECT query, mysql_stmt_affected_rows() was called prior to calling mysql_stmt_store_result(). Because mysql_stmt_affected_rows() returns an unsigned value, you can check for -1 by comparing the return value to (my_ulonglong)-1 (or to (my_ulonglong)~0, which is equivalent).

Errors

None.

Example

For the usage of mysql_stmt_affected_rows(), refer to the Example from section 20.2.7.4 mysql_stmt_execute().

20.2.7.13 mysql_stmt_close()

my_bool mysql_stmt_close(MYSQL_STMT *)

Description

Closes the prepared statement. mysql_stmt_close() also deallocates the statement handle pointed to by stmt.

If the current statement has pending or unread results, this function cancels them so that the next query can be executed.

Return Values

Zero if the statement was freed successfully. Non-zero if an error occurred.

Errors

CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_UNKNOWN_ERROR
An unknown error occurred.

Example

For the usage of mysql_stmt_close(), refer to the Example from section 20.2.7.4 mysql_stmt_execute().

20.2.7.14 mysql_stmt_data_seek()

void mysql_stmt_data_seek(MYSQL_STMT *stmt, my_ulonglong offset)

Description

Seeks to an arbitrary row in a statement result set. The offset value is a row number and should be in the range from 0 to mysql_stmt_num_rows(stmt)-1.

This function requires that the statement result set structure contains the entire result of the last executed query, so mysql_stmt_data_seek() may be used only in conjunction with mysql_stmt_store_result().

Return Values

None.

Errors

None.

20.2.7.15 mysql_stmt_errno()

unsigned int mysql_stmt_errno(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_errno() returns the error code for the most recently invoked statement API function that can succeed or fail. A return value of zero means that no error occurred. Client error message numbers are listed in the MySQL `errmsg.h' header file. Server error message numbers are listed in `mysqld_error.h'. In the MySQL source distribution you can find a complete list of error messages and error numbers in the file `Docs/mysqld_error.txt'. The server error codes also are listed at section 21.1 Error Returns.

Return Values

An error code value. Zero if no error occurred.

Errors

None.

20.2.7.16 mysql_stmt_error()

const char *mysql_stmt_error(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_error() returns a null-terminated string containing the error message for the most recently invoked statement API function that can succeed or fail. An empty string ("") is returned if no error occurred. This means the following two tests are equivalent:


if (mysql_stmt_errno(stmt))
{
  // an error occurred
}

if (mysql_stmt_error(stmt)[0])
{
  // an error occurred
}

The language of the client error messages may be changed by recompiling the MySQL client library. Currently you can choose error messages in several different languages.

Return Values

A character string that describes the error. An empty string if no error occurred.

Errors

None.

20.2.7.17 mysql_stmt_free_result()

my_bool mysql_stmt_free_result(MYSQL_STMT *stmt)

To be added.

Description

Return Values

Errors

20.2.7.18 mysql_stmt_num_rows()

my_ulonglong mysql_stmt_num_rows(MYSQL_STMT *stmt)

Description

Returns the number of rows in the result set.

The use of mysql_stmt_num_rows() depends on whether or not you used mysql_stmt_store_result() to buffer the entire result set in the statement handle.

If you use mysql_stmt_store_result(), mysql_stmt_num_rows() may be called immediately.

Return Values

The number of rows in the result set.

Errors

None.

20.2.7.19 mysql_stmt_reset()

my_bool mysql_stmt_reset(MYSQL_STMT *stmt)

Description

Reset prepared statement on client and server to state after prepare. For now this is mainly used to reset data sent with mysql_stmt_send_long_data().

To re-prepare the statement with another query, use mysql_stmt_prepare().

Return Values

Zero if the statement was reset successfully. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.7.20 mysql_stmt_row_seek()

MYSQL_ROW_OFFSET mysql_stmt_row_seek(MYSQL_STMT *stmt, MYSQL_ROW_OFFSET offset)

Description

Sets the row cursor to an arbitrary row in a statement result set. The offset value is a row offset that should be a value returned from mysql_stmt_row_tell() or from mysql_stmt_row_seek(). This value is not a row number; if you want to seek to a row within a result set by number, use mysql_stmt_data_seek() instead.

This function requires that the result set structure contains the entire result of the query, so mysql_stmt_row_seek() may be used only in conjunction with mysql_stmt_store_result().

Return Values

The previous value of the row cursor. This value may be passed to a subsequent call to mysql_stmt_row_seek().

Errors

None.

20.2.7.21 mysql_stmt_row_tell()

MYSQL_ROW_OFFSET mysql_stmt_row_tell(MYSQL_STMT *stmt)

Description

Returns the current position of the row cursor for the last mysql_stmt_fetch(). This value can be used as an argument to mysql_stmt_row_seek().

You should use mysql_stmt_row_tell() only after mysql_stmt_store_result().

Return Values

The current offset of the row cursor.

Errors

None.

20.2.7.22 mysql_stmt_sqlstate()

const char *mysql_stmt_sqlstate(MYSQL_STMT *stmt)

Description

For the statement specified by stmt, mysql_stmt_sqlstate() returns a null-terminated string containing the SQLSTATE error code for the most recently invoked prepared statement API function that can succeed or fail. The error code consists of five characters. "00000" means ``no error''. The values are specified by ANSI SQL and ODBC. For a list of possible values, see section 21.1 Error Returns.

Note that not all MySQL errors are yet mapped to SQLSTATE's. The value "HY000" (general error) is used for unmapped errors.

This function was added to MySQL 4.1.1.

Return Values

A null-terminated character string containing the SQLSTATE error code.

20.2.7.23 mysql_stmt_store_result()

int mysql_stmt_store_result(MYSQL_STMT *stmt)

Description

You must call mysql_stmt_store_result() for every query that successfully produces a result set (SELECT, SHOW, DESCRIBE, EXPLAIN), and only if you want to buffer the complete result set by the client, so that the subsequent mysql_stmt_fetch() call returns buffered data.

It is unnecessary to call mysql_stmt_store_result() for other queries, but if you do, it will not harm or cause any notable performance in all cases. You can detect whether the query produced a result set by checking if mysql_stmt_result_metadata() returns NULL. For more information, refer to section 20.2.7.7 mysql_stmt_result_metadata().

Return Values

Zero if the results are buffered successfully. Non-zero if an error occurred.

Errors

CR_COMMANDS_OUT_OF_SYNC
Commands were executed in an improper order.
CR_OUT_OF_MEMORY
Out of memory.
CR_SERVER_GONE_ERROR
The MySQL server has gone away.
CR_SERVER_LOST
The connection to the server was lost during the query.
CR_UNKNOWN_ERROR
An unknown error occurred.

20.2.8 C API Handling of Multiple Query Execution

From version 4.1, MySQL supports the execution of multiple statements specified in a single query string. To use this capability with a given connection, you must specify the CLIENT_MULTI_STATEMENTS option in the flags parameter of mysql_real_connect() when opening the connection. You can also set this for a connection by calling mysql_set_server_option(MYSQL_OPTION_MULTI_STATEMENTS_ON)

By default, mysql_query() and mysql_real_query() return only the first query status and the subsequent queries status can be processed using mysql_more_results() and mysql_next_result().


/* Connect to server with option CLIENT_MULTI_STATEMENTS */
mysql_real_connect(..., CLIENT_MULTI_STATEMENTS);

/* Now execute multiple queries */
mysql_query(mysql,"DROP TABLE IF EXISTS test_table;\
                   CREATE TABLE test_table(id INT);\
                   INSERT INTO test_table VALUES(10);\
                   UPDATE test_table SET id=20 WHERE id=10;\
                   SELECT * FROM test_table;\
                   DROP TABLE test_table";
do
{
  /* Process all results */
  ...
  printf("total affected rows: %lld", mysql_affected_rows(mysql));
  ...
  if (!(result= mysql_store_result(mysql)))
  {
     printf(stderr, "Got fatal error processing query\n");
     exit(1);
  }
  process_result_set(result);	/* client function */
  mysql_free_result(result);
} while (!mysql_next_result(mysql));

20.2.9 C API Handling of Date and Time Values

The new binary protocol available in MySQL 4.1 and above allows you to send and receive date and time values (DATE, TIME, DATETIME, and TIMESTAMP), using the MYSQL_TIME structure. The members of this structure are described in section 20.2.5 C API Prepared Statement Datatypes.

To send temporal data values, you create a prepared statement with mysql_stmt_prepare(). Then, before calling mysql_stmt_execute() to execute the statement, use the following procedure to set up each temporal parameter:

  1. In the MYSQL_BIND structure associated with the data value, set the buffer_type member to the type that indicates what kind of temporal value you're sending. For DATE, TIME, DATETIME, or TIMESTAMP values, set buffer_type to MYSQL_TYPE_DATE, MYSQL_TYPE_TIME, MYSQL_TYPE_DATETIME, or MYSQL_TYPE_TIMESTAMP, respectively.
  2. Set the buffer member of the MYSQL_BIND structure to the address of the MYSQL_TIME structure in which you will pass the temporal value.
  3. Fill in the members of the MYSQL_TIME structure that are appropriate for the type of temporal value you're passing.

Use mysql_stmt_bind_param() to bind the parameter data to the statement. Then you can call mysql_stmt_execute().

To retrieve temporal values, the procedure is similar, except that you set the buffer_type member to the type of value you expect to receive, and the buffer member to the address of a MYSQL_TIME structure into which the returned value should be placed. Use mysql_bind_results() to bind the buffers to the statement after calling mysql_stmt_execute() and before fetching the results.

Here is a simple example that inserts DATE, TIME, and TIMESTAMP data. The mysql variable is assumed to be a valid connection handle.


  MYSQL_TIME  ts;
  MYSQL_BIND  bind[3];
  MYSQL_STMT  *stmt;
  
  strmov(query, "INSERT INTO test_table(date_field, time_field,
                                        timestamp_field) VALUES(?,?,?");

  stmt = mysql_stmt_init(mysql);
  if (!stmt)
  {
    fprintf(stderr, " mysql_stmt_init(), out of memory\n");
    exit(0);
  }
  if (mysql_stmt_prepare(mysql, query, strlen(query)))
  {
    fprintf(stderr, "\n mysql_stmt_prepare(), INSERT failed");
    fprintf(stderr, "\n %s", mysql_stmt_error(stmt));
    exit(0);
  }

  /* setup input buffers for all 3 parameters */
  bind[0].buffer_type= MYSQL_TYPE_DATE;
  bind[0].buffer= (char *)&ts;  
  bind[0].is_null= 0;
  bind[0].length= 0;
  ..
  bind[1]= bind[2]= bind[0];
  ..

  mysql_stmt_bind_param(stmt, bind);

  /* supply the data to be sent is the ts structure */
  ts.year= 2002;
  ts.month= 02;
  ts.day= 03;

  ts.hour= 10;
  ts.minute= 45;
  ts.second= 20;

  mysql_stmt_execute(stmt);
  .. 

20.2.10 C API Threaded Function Descriptions

You need to use the following functions when you want to create a threaded client. See section 20.2.14 How to Make a Threaded Client.

20.2.10.1 my_init()

void my_init(void)

Description

This function needs to be called once in the program before calling any MySQL function. This initializes some global variables that MySQL needs. If you are using a thread-safe client library, this will also call mysql_thread_init() for this thread.

This is automatically called by mysql_init(), mysql_server_init() and mysql_connect().

Return Values

None.

20.2.10.2 mysql_thread_init()

my_bool mysql_thread_init(void)

Description

This function needs to be called for each created thread to initialize thread-specific variables.

This is automatically called by my_init() and mysql_connect().

Return Values

Zero if successful. Non-zero if an error occurred.

20.2.10.3 mysql_thread_end()

void mysql_thread_end(void)

Description

This function needs to be called before calling pthread_exit() to free memory allocated by mysql_thread_init().

Note that this function is not invoked automatically by the client library. It must be called explicitly to avoid a memory leak.

Return Values

None.

20.2.10.4 mysql_thread_safe()

unsigned int mysql_thread_safe(void)

Description

This function indicates whether the client is compiled as thread-safe.

Return Values

1 is the client is thread-safe, 0 otherwise.

20.2.11 C API Embedded Server Function Descriptions

You must use the following functions if you want to allow your application to be linked against the embedded MySQL server library. See section 20.2.15 libmysqld, the Embedded MySQL Server Library.

If the program is linked with -lmysqlclient instead of -lmysqld, these functions do nothing. This makes it possible to choose between using the embedded MySQL server and a stand-alone server without modifying any code.

20.2.11.1 mysql_server_init()

int mysql_server_init(int argc, char **argv, char **groups)

Description

This function must be called once in the program using the embedded server before calling any other MySQL function. It starts the server and initializes any subsystems (mysys, InnoDB, etc.) that the server uses. If this function is not called, the program will crash. If you are using the DBUG package that comes with MySQL, you should call this after you have called MY_INIT().

The argc and argv arguments are analogous to the arguments to main(). The first element of argv is ignored (it typically contains the program name). For convenience, argc may be 0 (zero) if there are no command-line arguments for the server. mysql_server_init() makes a copy of the arguments so it's safe to destroy argv or groups after the call.

The NULL-terminated list of strings in groups selects which groups in the option files will be active. See section 4.3.2 Using Option Files. For convenience, groups may be NULL, in which case the [server] and [emedded] groups will be active.

Example

#include <mysql.h>
#include <stdlib.h>

static char *server_args[] = {
  "this_program",       /* this string is not used */
  "--datadir=.",
  "--key_buffer_size=32M"
};
static char *server_groups[] = {
  "embedded",
  "server",
  "this_program_SERVER",
  (char *)NULL
};

int main(void) {
  if (mysql_server_init(sizeof(server_args) / sizeof(char *),
                        server_args, server_groups))
    exit(1);

  /* Use any MySQL API functions here */

  mysql_server_end();

  return EXIT_SUCCESS;
}

Return Values

0 if okay, 1 if an error occurred.

20.2.11.2 mysql_server_end()

void mysql_server_end(void)

Description

This function must be called once in the program after all other MySQL functions. It shuts down the embedded server.

Return Values

None.

20.2.12 Common questions and problems when using the C API

20.2.12.1 Why mysql_store_result() Sometimes Returns NULL After mysql_query() Returns Success

It is possible for mysql_store_result() to return NULL following a successful call to mysql_query(). When this happens, it means one of the following conditions occurred:

  • There was a malloc() failure (for example, if the result set was too large).
  • The data couldn't be read (an error occurred on the connection).
  • The query returned no data (for example, it was an INSERT, UPDATE, or DELETE).

You can always check whether the statement should have produced a non-empty result by calling mysql_field_count(). If mysql_field_count() returns zero, the result is empty and the last query was a statement that does not return values (for example, an INSERT or a DELETE). If mysql_field_count() returns a non-zero value, the statement should have produced a non-empty result. See the description of the mysql_field_count() function for an example.

You can test for an error by calling mysql_error() or mysql_errno().

20.2.12.2 What Results You Can Get from a Query

In addition to the result set returned by a query, you can also get the following information:

  • mysql_affected_rows() returns the number of rows affected by the last query when doing an INSERT, UPDATE, or DELETE. In MySQL 3.23, there is an exception when DELETE is used without a WHERE clause. In this case, the table is re-created as an empty table and mysql_affected_rows() returns zero for the number of records affected. In MySQL 4.0, DELETE always returns the correct number of rows deleted. For a fast recreate, use TRUNCATE TABLE.
  • mysql_num_rows() returns the number of rows in a result set. With mysql_store_result(), mysql_num_rows() may be called as soon as mysql_store_result() returns. With mysql_use_result(), mysql_num_rows() may be called only after you have fetched all the rows with mysql_fetch_row().
  • mysql_insert_id() returns the ID generated by the last query that inserted a row into a table with an AUTO_INCREMENT index. See section 20.2.3.32 mysql_insert_id().
  • Some queries (LOAD DATA INFILE ..., INSERT INTO ... SELECT ..., UPDATE) return additional information. The result is returned by mysql_info(). See the description for mysql_info() for the format of the string that it returns. mysql_info() returns a NULL pointer if there is no additional information.

20.2.12.3 How to Get the Unique ID for the Last Inserted Row

If you insert a record into a table that contains an AUTO_INCREMENT column, you can obtain the value stored into that column by calling the mysql_insert_id() function.

You can check whether a value was stored into an AUTO_INCREMENT column by executing the following code. This also checks if the query was an INSERT with an AUTO_INCREMENT index:

if (mysql_error(&mysql)[0] == 0 &&
    mysql_num_fields(result) == 0 &&
    mysql_insert_id(&mysql) != 0)
{
    used_id = mysql_insert_id(&mysql);
}

For more information, see section 20.2.3.32 mysql_insert_id().

When a new AUTO_INCREMENT value has been generated, you can also obtain it by executing a SELECT LAST_INSERT_ID() statement mysql_query() and retrieving the value from the result set returned by the statement.

For LAST_INSERT_ID(), the most recently generated ID is maintained in the server on a per-connection basis. It will not be changed by another client. It will not even be changed if you update another AUTO_INCREMENT column with a non-magic value (that is, a value that is not NULL and not 0).

If you want to use the ID that was generated for one table and insert it into a second table, you can use SQL statements like this:

INSERT INTO foo (auto,text)
    VALUES(NULL,'text');              # generate ID by inserting NULL
INSERT INTO foo2 (id,text)
    VALUES(LAST_INSERT_ID(),'text');  # use ID in second table

Note that mysql_insert_id() returns the value stored into an AUTO_INCREMENT column, whether that value is automatically generated by storing NULL or 0 or is an explicit value. LAST_INSERT_ID() returns automatically generated AUTO_INCREMENT values. If you store an explicit value other than NULL or 0, it does not affect the value returned by LAST_INSERT_ID().

20.2.12.4 Problems Linking with the C API

When linking with the C API, the following errors may occur on some systems:

gcc -g -o client test.o -L/usr/local/lib/mysql -lmysqlclient -lsocket -lnsl

Undefined        first referenced
 symbol          in file
floor            /usr/local/lib/mysql/libmysqlclient.a(password.o)
ld: fatal: Symbol referencing errors. No output written to client

If this happens on your system, you must include the math library by adding -lm to the end of the compile/link line.

20.2.13 Building Client Programs

If you compile MySQL clients that you've written yourself or that you obtain from a third-party, they must be linked using the -lmysqlclient -lz option on the link command. You may also need to specify a -L option to tell the linker where to find the library. For example, if the library is installed in `/usr/local/mysql/lib', use -L/usr/local/mysql/lib -lmysqlclient -lz on the link command.

For clients that use MySQL header files, you may need to specify a -I option when you compile them (for example, -I/usr/local/mysql/include), so the compiler can find the header files.

To make it simpler to compile MySQL programs on Unix, we have provided the mysql_config script for you. See section 20.1.2 mysql_config, Get compile options for compiling clients.

You can use it to compile a MySQL client as follows:

CFG=/usr/local/mysql/bin/mysql_config
sh -c "gcc -o progname `$CFG --cflags` progname.c `$CFG --libs`"

The sh -c is need to get the shell to not threat the output from mysql_config as one word.

20.2.14 How to Make a Threaded Client

The client library is almost thread-safe. The biggest problem is that the subroutines in `net.c' that read from sockets are not interrupt safe. This was done with the thought that you might want to have your own alarm that can break a long read to a server. If you install interrupt handlers for the SIGPIPE interrupt, the socket handling should be thread-safe.

New in 4.0.16: To not abort the program when a connection terminates, MySQL blocks SIGPIPE on the first call to mysql_server_init(), mysql_init() or mysql_connect(). If you want to have your own SIGPIPE handler, you should first call mysql_server_init() and then install your handler. In older versions of MySQL SIGPIPE was blocked, but only in the thread safe client library, for every call to mysql_init().

In the older binaries we distribute on our Web site (http://www.mysql.com/), the client libraries are not normally compiled with the thread-safe option (the Windows binaries are by default compiled to be thread-safe). Newer binary distributions should have both a normal and a thread-safe client library.

To get a threaded client where you can interrupt the client from other threads and set timeouts when talking with the MySQL server, you should use the -lmysys, -lmystrings, and -ldbug libraries and the net_serv.o code that the server uses.

If you don't need interrupts or timeouts, you can just compile a thread-safe client library (mysqlclient_r) and use this. See section 20.2 MySQL C API. In this case you don't have to worry about the net_serv.o object file or the other MySQL libraries.

When using a threaded client and you want to use timeouts and interrupts, you can make great use of the routines in the `thr_alarm.c' file. If you are using routines from the mysys library, the only thing you must remember is to call my_init() first! See section 20.2.10 C API Threaded Function Descriptions.

All functions except mysql_real_connect() are by default thread-safe. The following notes describe how to compile a thread-safe client library and use it in a thread-safe manner. (The notes below for mysql_real_connect() actually apply to mysql_connect() as well, but because mysql_connect() is deprecated, you should be using mysql_real_connect() anyway.)

To make mysql_real_connect() thread-safe, you must recompile the client library with this command:

shell> ./configure --enable-thread-safe-client

This will create a thread-safe client library libmysqlclient_r. (Assuming your OS has a thread-safe gethostbyname_r() function.) This library is thread-safe per connection. You can let two threads share the same connection with the following caveats:

  • Two threads can't send a query to the MySQL server at the same time on the same connection. In particular, you have to ensure that between a mysql_query() and mysql_store_result() no other thread is using the same connection.
  • Many threads can access different result sets that are retrieved with mysql_store_result().
  • If you use mysql_use_result, you have to ensure that no other thread is using the same connection until the result set is closed. However, it really is best for threaded clients that share the same connection to use mysql_store_result().
  • If you want to use multiple threads on the same connection, you must have a mutex lock around your mysql_query() and mysql_store_result() call combination. Once mysql_store_result() is ready, the lock can be released and other threads may query the same connection.
  • If you program with POSIX threads, you can use pthread_mutex_lock() and pthread_mutex_unlock() to establish and release a mutex lock.

You need to know the following if you have a thread that is calling MySQL functions which did not create the connection to the MySQL database:

When you call mysql_init() or mysql_connect(), MySQL will create a thread-specific variable for the thread that is used by the debug library (among other things).

If you call a MySQL function, before the thread has called mysql_init() or mysql_connect(), the thread will not have the necessary thread-specific variables in place and you are likely to end up with a core dump sooner or later.

The get things to work smoothly you have to do the following:

  1. Call my_init() at the start of your program if it calls any other MySQL function before calling mysql_real_connect().
  2. Call mysql_thread_init() in the thread handler before calling any MySQL function.
  3. In the thread, call mysql_thread_end() before calling pthread_exit(). This will free the memory used by MySQL thread-specific variables.

You may get some errors because of undefined symbols when linking your client with libmysqlclient_r. In most cases this is because you haven't included the thread libraries on the link/compile line.

20.2.15 libmysqld, the Embedded MySQL Server Library

20.2.15.1 Overview of the Embedded MySQL Server Library

The embedded MySQL server library makes it possible to run a full-featured MySQL server inside a client application. The main benefits are increased speed and more simple management for embedded applications.

The embedded server library is based on the client/server version of MySQL, which is written in C/C++. Consequently, the embedded server also is written in C/C++. There is no embedded server available in other languages.

The API is identical for the embedded MySQL version and the client/server version. To change an old threaded application to use the embedded library, you normally only have to add calls to the following functions:

Function When to Call
mysql_server_init() Should be called before any other MySQL function is called, preferably early in the main() function.
mysql_server_end() Should be called before your program exits.
mysql_thread_init() Should be called in each thread you create that will access MySQL.
mysql_thread_end() Should be called before calling pthread_exit()

Then you must link your code with `libmysqld.a' instead of `libmysqlclient.a'.

The mysql_server_xxx functions are also included in `libmysqlclient.a' to allow you to change between the embedded and the client/server version by just linking your application with the right library. See section 20.2.11.1 mysql_server_init().

20.2.15.2 Compiling Programs with libmysqld

To get a libmysqld library you should configure MySQL with the --with-embedded-server option.

When you link your program with libmysqld, you must also include the system-specific pthread libraries and some libraries that the MySQL server uses. You can get the full list of libraries by executing mysql_config --libmysqld-libs.

The correct flags for compiling and linking a threaded program must be used, even if you do not directly call any thread functions in your code.

20.2.15.3 Restrictions when using the Embedded MySQL Server

The embedded server has the following limitations:

  • No support for ISAM tables. (This is mainly done to make the library smaller)
  • No user-defined functions (UDFs).
  • No stack trace on core dump.
  • No internal RAID support. (This is not normally needed as most OS has nowadays support for big files).
  • You cannot set this up as a master or a slave (no replication).
  • You can't connect to an embedded server from an outside process with sockets or TCP/IP.

Some of these limitations can be changed by editing the `mysql_embed.h' include file and recompiling MySQL.

20.2.15.4 Using Option Files with the Embedded Server

The following is the recommended way to use option files to make it easy to switch between a client/server application and one where MySQL is embedded. See section 4.3.2 Using Option Files.

  • Put common options in the [server] section. These will be read by both MySQL versions.
  • Put client/server-specific options in the [mysqld] section.
  • Put embedded MySQL-specific options in the [embedded] section.
  • Put application-specific options in a [ApplicationName_SERVER] section.

20.2.15.5 Things left to do in Embedded Server (TODO)

  • We are going to provide options to leave out some parts of MySQL to make the library smaller.
  • There is still a lot of speed optimization to do.
  • Errors are written to stderr. We will add an option to specify a filename for these.
  • We have to change InnoDB to not be so verbose when using in the embedded version.

20.2.15.6 A Simple Embedded Server Example

This example program and makefile should work without any changes on a Linux or FreeBSD system. For other operating systems, minor changes will be needed. This example is designed to give enough details to understand the problem, without the clutter that is a necessary part of a real application.

To try out the example, create an `test_libmysqld' directory at the same level as the mysql-4.0 source directory. Save the `test_libmysqld.c' source and the `GNUmakefile' in the directory, and run GNU `make' from inside the `test_libmysqld' directory.

`test_libmysqld.c'

/*
 * A simple example client, using the embedded MySQL server library
 */

#include <mysql.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>

MYSQL *db_connect(const char *dbname);
void db_disconnect(MYSQL *db);
void db_do_query(MYSQL *db, const char *query);

const char *server_groups[] = {
  "test_libmysqld_SERVER", "embedded", "server", NULL
};

int
main(int argc, char **argv)
{
  MYSQL *one, *two;

  /* mysql_server_init() must be called before any other mysql
   * functions.
   *
   * You can use mysql_server_init(0, NULL, NULL), and it will
   * initialize the server using groups = {
   *   "server", "embedded", NULL
   *  }.
   *
   * In your $HOME/.my.cnf file, you probably want to put:

[test_libmysqld_SERVER]
language = /path/to/source/of/mysql/sql/share/english

   * You could, of course, modify argc and argv before passing
   * them to this function.  Or you could create new ones in any
   * way you like.  But all of the arguments in argv (except for
   * argv[0], which is the program name) should be valid options
   * for the MySQL server.
   *
   * If you link this client against the normal mysqlclient
   * library, this function is just a stub that does nothing.
   */
  mysql_server_init(argc, argv, (char **)server_groups);

  one = db_connect("test");
  two = db_connect(NULL);

  db_do_query(one, "SHOW TABLE STATUS");
  db_do_query(two, "SHOW DATABASES");

  mysql_close(two);
  mysql_close(one);

  /* This must be called after all other mysql functions */
  mysql_server_end();

  exit(EXIT_SUCCESS);
}

static void
die(MYSQL *db, char *fmt, ...)
{
  va_list ap;
  va_start(ap, fmt);
  vfprintf(stderr, fmt, ap);
  va_end(ap);
  (void)putc('\n', stderr);
  if (db)
    db_disconnect(db);
  exit(EXIT_FAILURE);
}

MYSQL *
db_connect(const char *dbname)
{
  MYSQL *db = mysql_init(NULL);
  if (!db)
    die(db, "mysql_init failed: no memory");
  /*
   * Notice that the client and server use separate group names.
   * This is critical, because the server will not accept the
   * client's options, and vice versa.
   */
  mysql_options(db, MYSQL_READ_DEFAULT_GROUP, "test_libmysqld_CLIENT");
  if (!mysql_real_connect(db, NULL, NULL, NULL, dbname, 0, NULL, 0))
    die(db, "mysql_real_connect failed: %s", mysql_error(db));

  return db;
}

void
db_disconnect(MYSQL *db)
{
  mysql_close(db);
}

void
db_do_query(MYSQL *db, const char *query)
{
  if (mysql_query(db, query) != 0)
    goto err;

  if (mysql_field_count(db) > 0)
  {
    MYSQL_RES   *res;
    MYSQL_ROW    row, end_row;
    int num_fields;

    if (!(res = mysql_store_result(db)))
      goto err;
    num_fields = mysql_num_fields(res);
    while ((row = mysql_fetch_row(res)))
    {
      (void)fputs(">> ", stdout);
      for (end_row = row + num_fields; row < end_row; ++row)
        (void)printf("%s\t", row ? (char*)*row : "NULL");
      (void)fputc('\n', stdout);
    }
    (void)fputc('\n', stdout);
    mysql_free_result(res);
  }
  else
    (void)printf("Affected rows: %lld\n", mysql_affected_rows(db));

  return;

err:
  die(db, "db_do_query failed: %s [%s]", mysql_error(db), query);
}

`GNUmakefile'

# This assumes the MySQL software is installed in /usr/local/mysql
inc      := /usr/local/mysql/include/mysql
lib      := /usr/local/mysql/lib

# If you have not installed the MySQL software yet, try this instead
#inc      := $(HOME)/mysql-4.0/include
#lib      := $(HOME)/mysql-4.0/libmysqld

CC       := gcc
CPPFLAGS := -I$(inc) -D_THREAD_SAFE -D_REENTRANT
CFLAGS   := -g -W -Wall
LDFLAGS  := -static
# You can change -lmysqld to -lmysqlclient to use the
# client/server library
LDLIBS    = -L$(lib) -lmysqld -lz -lm -lcrypt

ifneq (,$(shell grep FreeBSD /COPYRIGHT 2>/dev/null))
# FreeBSD
LDFLAGS += -pthread
else
# Assume Linux
LDLIBS += -lpthread
endif

# This works for simple one-file test programs
sources := $(wildcard *.c)
objects := $(patsubst %c,%o,$(sources))
targets := $(basename $(sources))

all: $(targets)

clean:
        rm -f $(targets) $(objects) *.core

20.2.15.7 Licensing the Embedded Server

The MySQL source code is covered by the GNU GPL license (see section G GNU General Public License). One result of this is that any program which includes, by linking with libmysqld, the MySQL source code must be released as free software (under a license compatible with the GPL).

We encourage everyone to promote free software by releasing code under the GPL or a compatible license. For those who are not able to do this, another option is to purchase a commercial license for the MySQL code from MySQL AB. For details, please see section 1.4.3 MySQL Licenses.

20.3 MySQL ODBC Support

MySQL provides support for ODBC by means of the MyODBC program. This chapter will teach you how to install MyODBC, and how to use it. Here, you will also find a list of common programs that are known to work with MyODBC.

20.3.1 How to Install MyODBC

MyODBC 2.50 is a 32-bit ODBC 2.50 specification level 0 (with level 1 and level 2 features) driver for connecting an ODBC-aware application to MySQL. MyODBC works on Windows 9x, Me, NT, 2000, and XP, and on most Unix platforms. MyODBC 3.51 is an enhanced version with ODBC 3.5x specification level 1 (complete core API + level 2 features).

MyODBC is Open Source, and you can find the newest version at http://www.mysql.com/downloads/api-myodbc.php. Please note that the 2.50.x versions are LGPL licensed, whereas the 3.51.x versions are GPL licensed.

If you have problem with MyODBC and your program also works with OLEDB, you should try the OLEDB driver.

Normally you only need to install MyODBC on Windows machines. You only need MyODBC for Unix if you have a program like ColdFusion that is running on the Unix machine and uses ODBC to connect to the databases.

If you want to install MyODBC on a Unix box, you will also need an ODBC manager. MyODBC is known to work with most of the Unix ODBC managers.

To install MyODBC on Windows, you should download the appropriate MyODBC `.zip' file, unpack it with WinZip or some similar program, and execute the `SETUP.EXE' file.

On Windows, NT, and XP you may get the following error when trying to install MyODBC:

An error occurred while copying C:\WINDOWS\SYSTEM\MFC30.DLL. Restart
Windows and try installing again (before running any applications which
use ODBC)

The problem in this case is that some other program is using ODBC and because of how Windows is designed, you may not in this case be able to install a new ODBC drivers with Microsoft's ODBC setup program. In most cases you can continue by just pressing Ignore to copy the rest of the MyODBC files and the final installation should still work. If this doesn't work, the solution is to restart your computer in ``safe mode`` (Choose this by pressing F8 just before your machine starts Windows while restarting), install MyODBC, and restart to normal mode.

  • To make a connection to a Unix box from a Windows box, with an ODBC application (one that doesn't support MySQL natively), you must first install MyODBC on the Windows machine.
  • The user and Windows machine must have the access privileges to the MySQL server on the Unix machine. This is set up with the GRANT command. See section 14.5.1.2 GRANT and REVOKE Syntax.
  • You must create an ODBC DSN entry as follows:
  • Now start your application and select the ODBC driver with the DSN you specified in the ODBC administrator.

Notice that there are other configuration options on the screen of MySQL (trace, don't prompt on connect, etc) that you can try if you run into problems.

20.3.2 How to Fill in the Various Fields in the ODBC Administrator Program

There are three possibilities for specifying the server name on Windows:

  • Use the IP address of the server.
  • Add a file `\windows\lmhosts' with the following information:
    ip hostname
    
    For example:
    194.216.84.21 my_hostname
    
  • Configure the PC to use DNS.

Example of how to fill in the ODBC setup:

Windows DSN name:   test
Description:        This is my test database
MySQL Database:     test
Server:             194.216.84.21
User:               monty
Password:           my_password
Port:

The value for the Windows DSN name field is any name that is unique in your Windows ODBC setup.

You don't have to specify values for the Server, User, Password, or Port fields in the ODBC setup screen. However, if you do, the values will be used as the defaults later when you attempt to make a connection. You have the option of changing the values at that time.

If the port number is not given, the default port (3306) is used.

If you specify the option Read options from C:\my.cnf, the groups client and odbc will be read from the `C:\my.cnf' file. You can use all options that are usable by mysql_options(). See section 20.2.3.40 mysql_options().

20.3.3 Connect parameters for MyODBC

One can specify the following parameters for MyODBC on the [Servername] section of an `ODBC.INI' file or through the InConnectionString argument in the SQLDriverConnect() call.

Parameter Default Value Comment
user ODBC (on Windows) The username used to connect to MySQL.
server localhost The hostname of the MySQL server.
database The default database.
option 0 A integer by which you can specify how MyODBC should work. See below.
port 3306 The TCP/IP port to use if server is not localhost.
stmt A statement that will be executed when connecting to MySQL
password The password for the server user combination.
socket The socket or Windows pipe to connect to.

The option argument is used to tell MyODBC that the client isn't 100% ODBC compliant. On Windows, one normally sets the option flag by toggling the different options on the connection screen but one can also set this in the option argument. The following options are listed in the same order as they appear in the MyODBC connect screen:

Bit Description
1 The client can't handle that MyODBC returns the real width of a column.
2 The client can't handle that MySQL returns the true value of affected rows. If this flag is set then MySQL returns 'found rows' instead. You must have MySQL 3.21.14 or newer to get this to work.
4 Make a debug log in c:\myodbc.log. This is the same as putting MYSQL_DEBUG=d:t:O,c::\myodbc.log in `AUTOEXEC.BAT'
8 Don't set any packet limit for results and parameters.
16 Don't prompt for questions even if driver would like to prompt
32 Simulate a ODBC 1.0 driver in some context.
64 Ignore use of database name in 'database.table.column'.
128 Force use of ODBC manager cursors (experimental).
256 Disable the use of extended fetch (experimental).
512 Pad CHAR fields to full column length.
1024 SQLDescribeCol() will return fully qualified column names
2048 Use the compressed client/server protocol
4096 Tell server to ignore space after function name and before '(' (needed by PowerBuilder). This will make all function names keywords!
8192 Connect with named pipes to a mysqld server running on NT.
16384 Change LONGLONG columns to INT columns (some applications can't handle LONGLONG).
32768 Return 'user' as Table_qualifier and Table_owner from SQLTables (experimental)
65536 Read parameters from the client and odbc groups from `my.cnf'
131072 Add some extra safety checks (should not bee needed but...)

If you want to have many options, you should add together their values. For example setting option to 12 (4+8) gives you debugging without package limits!

The default `MYODBC.DLL' is compiled for optimal performance. If you want to debug MyODBC (for example to enable tracing), you should instead use `MYODBCD.DLL'. To install this file, copy `MYODBCD.DLL' over the installed `MYODBC.DLL' file.

20.3.4 How to Report Problems with MyODBC

MyODBC has been tested with Access, Admndemo.exe, C++-Builder, Borland Builder 4, Centura Team Developer (formerly Gupta SQL/Windows), ColdFusion (on Solaris and NT with svc pack 5), Crystal Reports, DataJunction, Delphi, ERwin, Excel, iHTML, FileMaker Pro, FoxPro, Notes 4.5/4.6, SBSS, Perl DBD-ODBC, Paradox, Powerbuilder, Powerdesigner 32 bit, VC++, and Visual Basic.

If you know of any other applications that work with MyODBC, please send mail to the myodbc mailing list about this! See section 1.7.1.1 The MySQL Mailing Lists.

With some programs you may get an error like: Another user has modifies the record that you have modified. In most cases this can be solved by doing one of the following things:

  • Add a primary key for the table if there isn't one already.
  • Add a timestamp column if there isn't one already.
  • Only use double float fields. Some programs may fail when they compare single floats.

If these strategies don't help, you should generate a MyODBC trace file and try to figure out why things go wrong.

20.3.5 Programs Known to Work with MyODBC

Most programs should work with MyODBC, but for each of those listed here, we have tested it ourselves or received confirmation from some user that it works:

Program
Comment
Access
To make Access work:
  • If you are using Access 2000, you should get and install the newest (version 2.6 or above) Microsoft MDAC (Microsoft Data Access Components) from http://www.microsoft.com/data/. This will fix the following bug in Access: when you export data to MySQL, the table and column names aren't specified. Another way to around this bug is to upgrade to MyODBC Version 2.50.33 and MySQL Version 3.23.x, which together provide a workaround for this bug! You should also get and apply the Microsoft Jet 4.0 Service Pack 5 (SP5) which can be found here http://support.microsoft.com/support/kb/articles/Q 239/1/14.ASP. This will fix some cases where columns are marked as #deleted# in Access. Note that if you are using MySQL Version 3.22, you must to apply the MDAC patch and use MyODBC 2.50.32 or 2.50.34 and above to work around this problem.
  • For all Access versions, you should enable the MyODBC option flag Return matching rows. For Access 2.0, you should additionally enable Simulate ODBC 1.0.
  • You should have a timestamp in all tables you want to be able to update. For maximum portability TIMESTAMP(14) or simple TIMESTAMP is recommended instead of other TIMESTAMP(X) variations.
  • You should have a primary key in the table. If not, new or updated rows may show up as #DELETED#.
  • Only use DOUBLE float fields. Access fails when comparing with single floats. The symptom usually is that new or updated rows may show up as #DELETED# or that you can't find or update rows.
  • If you are linking a table through MyODBC, which has BIGINT as one of the column, then the results will be displayed as #DELETED. The work around solution is:
    • Have one more dummy column with TIMESTAMP as the datatype, preferably TIMESTAMP(14).
    • Check the 'Change BIGINT columns to INT' in connection options dialog in ODBC DSN Administrator
    • Delete the table link from access and re-create it.
    It still displays the previous records as #DELETED#, but newly added/updated records will be displayed properly.
  • If you still get the error Another user has changed your data after adding a TIMESTAMP column, the following trick may help you: Don't use table data sheet view. Create instead a form with the fields you want, and use that form data sheet view. You should set the DefaultValue property for the TIMESTAMP column to NOW(). It may be a good idea to hide the TIMESTAMP column from view so your users are not confused.
  • In some cases, Access may generate illegal SQL queries that MySQL can't understand. You can fix this by selecting "Query|SQLSpecific|Pass-Through" from the Access menu.
  • Access on NT will report BLOB columns as OLE OBJECTS. If you want to have MEMO columns instead, you should change the column to TEXT with ALTER TABLE.
  • Access can't always handle DATE columns properly. If you have a problem with these, change the columns to DATETIME.
  • If you have in Access a column defined as BYTE, Access will try to export this as TINYINT instead of TINYINT UNSIGNED. This will give you problems if you have values > 127 in the column!
ADO
When you are coding with the ADO API and MyODBC you need to put attention in some default properties that aren't supported by the MySQL server. For example, using the CursorLocation Property as adUseServer will return for the RecordCount Property a result of -1. To have the right value, you need to set this property to adUseClient, like is showing in the VB code here:
Dim myconn As New ADODB.Connection
Dim myrs As New Recordset
Dim mySQL As String
Dim myrows As Long

myconn.Open "DSN=MyODBCsample"
mySQL = "SELECT * from user"
myrs.Source = mySQL
Set myrs.ActiveConnection = myconn
myrs.CursorLocation = adUseClient
myrs.Open
myrows = myrs.RecordCount

myrs.Close
myconn.Close
Another workaround is to use a SELECT COUNT(*) statement for a similar query to get the correct row count.
Active server pages (ASP)
You should use the option flag Return matching rows.
BDE applications
To get these to work, you should set the option flags Don't optimize column widths and Return matching rows.
Borland Builder 4
When you start a query you can use the property Active or use the method Open. Note that Active will start by automatically issuing a SELECT * FROM ... query that may not be a good thing if your tables are big!
ColdFusion (On Unix)
The following information is taken from the ColdFusion documentation: Use the following information to configure ColdFusion Server for Linux to use the unixODBC driver with MyODBC for MySQL data sources. Allaire has verified that MyODBC Version 2.50.26 works with MySQL Version 3.22.27 and ColdFusion for Linux. (Any newer version should also work.) You can download MyODBC at http://www.mysql.com/downloads/api-myodbc.php ColdFusion Version 4.5.1 allows you to us the ColdFusion Administrator to add the MySQL data source. However, the driver is not included with ColdFusion Version 4.5.1. Before the MySQL driver will appear in the ODBC datasources drop-down list, you must build and copy the MyODBC driver to `/opt/coldfusion/lib/libmyodbc.so'. The Contrib directory contains the program `mydsn-xxx.zip' which allows you to build and remove the DSN registry file for the MyODBC driver on Coldfusion applications.
DataJunction
You have to change it to output VARCHAR rather than ENUM, as it exports the latter in a manner that causes MySQL grief.
Excel
Works. A few tips:
  • If you have problems with dates, try to select them as strings using the CONCAT() function. For example:
    select CONCAT(rise_time), CONCAT(set_time)
        from sunrise_sunset;
    
    Values retrieved as strings this way should be correctly recognized as time values by Excel97. The purpose of CONCAT() in this example is to fool ODBC into thinking the column is of ``string type''. Without the CONCAT(), ODBC knows the column is of time type, and Excel does not understand that. Note that this is a bug in Excel, because it automatically converts a string to a time. This would be great if the source was a text file, but is plain stupid when the source is an ODBC connection that reports exact types for each column.
Word
To retrieve data from MySQL to Word/Excel documents, you need to use the MyODBC driver and the Add-in Microsoft Query help. For example, create a db with a table containing 2 columns of text:
  • Insert rows using the mysql client command-line tool.
  • Create a DSN file using the ODBC manager, for example, `my' for the db above.
  • Open the Word application.
  • Create a blank new documentation.
  • Using the tool bar called Database, press the button insert database.
  • Press the button Get Data.
  • At the right hand of the screen Get Data, press the button Ms Query.
  • In the Ms Query create a New Data Source using the DSN file my.
  • Select the new query.
  • Select the columns that you want.
  • Make a filter if you want.
  • Make a Sort if you want.
  • Select Return Data to Microsoft Word.
  • Click Finish.
  • Click Insert data and select the records.
  • Click OK and you see the rows in your Word document.
odbcadmin
Test program for ODBC.
Delphi
You must use BDE Version 3.2 or newer. Set the Don't optimize column width option field when connecting to MySQL. Also, here is some potentially useful Delphi code that sets up both an ODBC entry and a BDE entry for MyODBC (the BDE entry requires a BDE Alias Editor that is free at a Delphi Super Page near you. (Thanks to Bryan Brunton bryan@flesherfab.com for this):
fReg:= TRegistry.Create;
  fReg.OpenKey('\Software\ODBC\ODBC.INI\DocumentsFab', True);
  fReg.WriteString('Database', 'Documents');
  fReg.WriteString('Description', ' ');
  fReg.WriteString('Driver', 'C:\WINNT\System32\myodbc.dll');
  fReg.WriteString('Flag', '1');
  fReg.WriteString('Password', '');
  fReg.WriteString('Port', ' ');
  fReg.WriteString('Server', 'xmark');
  fReg.WriteString('User', 'winuser');
  fReg.OpenKey('\Software\ODBC\ODBC.INI\ODBC Data Sources', True);
  fReg.WriteString('DocumentsFab', 'MySQL');
  fReg.CloseKey;
  fReg.Free;

  Memo1.Lines.Add('DATABASE NAME=');
  Memo1.Lines.Add('USER NAME=');
  Memo1.Lines.Add('ODBC DSN=DocumentsFab');
  Memo1.Lines.Add('OPEN MODE=READ/WRITE');
  Memo1.Lines.Add('BATCH COUNT=200');
  Memo1.Lines.Add('LANGDRIVER=');
  Memo1.Lines.Add('MAX ROWS=-1');
  Memo1.Lines.Add('SCHEMA CACHE DIR=');
  Memo1.Lines.Add('SCHEMA CACHE SIZE=8');
  Memo1.Lines.Add('SCHEMA CACHE TIME=-1');
  Memo1.Lines.Add('SQLPASSTHRU MODE=SHARED AUTOCOMMIT');
  Memo1.Lines.Add('SQLQRYMODE=');
  Memo1.Lines.Add('ENABLE SCHEMA CACHE=FALSE');
  Memo1.Lines.Add('ENABLE BCD=FALSE');
  Memo1.Lines.Add('ROWSET SIZE=20');
  Memo1.Lines.Add('BLOBS TO CACHE=64');
  Memo1.Lines.Add('BLOB SIZE=32');

  AliasEditor.Add('DocumentsFab','MySQL',Memo1.Lines);
C++ Builder
Tested with BDE Version 3.0. The only known problem is that when the table schema changes, query fields are not updated. BDE, however, does not seem to recognize primary keys, only the index PRIMARY, though this has not been a problem.
Vision
You should use the option flag Return matching rows.
Visual Basic
To be able to update a table, you must define a primary key for the table. Visual Basic with ADO can't handle big integers. This means that some queries like SHOW PROCESSLIST will not work properly. The fix is to set the option OPTION=16384 in the ODBC connect string or to set the Change BIGINT columns to INT option in the MyODBC connect screen. You may also want to set the Return matching rows option.
VisualInterDev
If you get the error [Microsoft][ODBC Driver Manager] Driver does not support this parameter the reason may be that you have a BIGINT in your result. Try setting the Change BIGINT columns to INT option in the MyODBC connect screen.
Visual Objects
You should use the option flag Don't optimize column widths.

20.3.6 How to Get the Value of an AUTO_INCREMENT Column in ODBC

A common problem is how to get the value of an automatically generated ID from an INSERT. With ODBC, you can do something like this (assuming that auto is an AUTO_INCREMENT field):

INSERT INTO foo (auto,text) VALUES(NULL,'text');
SELECT LAST_INSERT_ID();

Or, if you are just going to insert the ID into another table, you can do this:

INSERT INTO foo (auto,text) VALUES(NULL,'text');
INSERT INTO foo2 (id,text) VALUES(LAST_INSERT_ID(),'text');

See section 20.2.12.3 How to Get the Unique ID for the Last Inserted Row.

For the benefit of some ODBC applications (at least Delphi and Access), the following query can be used to find a newly inserted row:

SELECT * FROM tbl_name WHERE auto IS NULL;

20.3.7 Reporting Problems with MyODBC

If you encounter difficulties with MyODBC, you should start by making a log file from the ODBC manager (the log you get when requesting logs from ODBCADMIN) and a MyODBC log.

To get a MyODBC log, you need to do the following:

  1. Ensure that you are using `myodbcd.dll' and not `myodbc.dll'. The easiest way to do this is to get `myodbcd.dll' from the MyODBC distribution and copy it over the `myodbc.dll', which is probably in your `C:\windows\system32' or `C:\winnt\system32' directory. Note that you probably want to restore the old `myodbc.dll' file when you have finished testing, as it is a lot faster than `myodbcd.dll'.
  2. Select the ``Trace MyODBC'' option in the MyODBC connect/configure screen. The log will be written to the file `C:\myodbc.log'. If the trace option is not remembered the next time you visit this screen, it means that you are not using the myodbcd.dll driver. Reread the previous step to verify that you have installed `myodbcd.dll'.
  3. Start your application and try to get it to fail.

Check the MyODBC trace file, to find out what could be wrong. You should be able to determine what statements were issued by searching for the string >mysql_real_query in the `myodbc.log' file.

You should also try issuing the statements from the mysql client program or from admndemo. This will help you determine whether the error is in MyODBC or MySQL.

If you find out something is wrong, please only send the relevant rows (maximum 40 rows) to the myodbc mailing list. See section 1.7.1.1 The MySQL Mailing Lists. Please never send the whole MyODBC or ODBC log file!

If you are unable to find out what's wrong, the last option is to make an archive in tar or ZIP format that contains a MyODBC trace file, the ODBC log file, and a `README' file that explains the problem. You can send this to ftp://support.mysql.com/pub/mysql/secret/. Only we at MySQL AB will have access to the files you upload, and we will be very discreet with the data!

If you can create a program that also demonstrates the problem, please include it in the archive as well.

If the program works with some other SQL server, you should include an ODBC log file where you do exactly the same thing in the other SQL server.

Remember that the more information you can supply to us, the more likely it is that we can fix the problem!

20.4 MySQL Java Connectivity (JDBC)

There are 2 supported JDBC drivers for MySQL:

For more information, consult any general JDBC documentation, plus each driver's own documentation for MySQL-specific features.

Documentation for MySQL Connector/J is available online at the MySQL AB Web site at http://www.mysql.com/documentation/.

20.5 MySQL PHP API

PHP is a server-side, HTML-embedded scripting language that may be used to create dynamic Web pages. It contains support for accessing several databases, including MySQL. PHP may be run as a separate program or compiled as a module for use with the Apache Web server.

The distribution and documentation are available at the PHP Web site (http://www.php.net/).

20.5.1 Common Problems with MySQL and PHP

  • Error: "Maximum Execution Time Exceeded" This is a PHP limit; go into the `php.ini' file and set the maximum execution time up from 30 seconds to something higher, as needed. It is also not a bad idea to double the RAM allowed per script to 16MB instead of 8MB.
  • Error: "Fatal error: Call to unsupported or undefined function mysql_connect() in .." This means that your PHP version isn't compiled with MySQL support. You can either compile a dynamic MySQL module and load it into PHP or recompile PHP with built-in MySQL support. This is described in detail in the PHP manual.
  • Error: "undefined reference to `uncompress'" This means that the client library is compiled with support for a compressed client/server protocol. The fix is to add -lz last when linking with -lmysqlclient.

20.6 MySQL Perl API

The Perl DBI module provides a generic interface for database access. You can write a DBI script that works with many different database engines without change. To use DBI, you must install the DBI module, as well as a DataBase Driver (DBD) module for each type of server you want to access. For MySQL, this driver is the DBD::mysql module.

Perl DBI is now the recommended Perl interface. It replaces an older interface called mysqlperl, which should be considered obsolete.

Installation instructions for Perl DBI support are given in section 2.7 Perl Installation Notes.

DBI information is available at the command line, online, or in printed form:

  • Once you have the DBI and DBD::mysql modules installed, you can get information about them at the command line with the perldoc command:
    shell> perldoc DBI
    shell> perldoc DBI::FAQ
    shell> perldoc DBD::mysql
    
    You can also use pod2man, pod2html, and so forth to translate this information into other formats.
  • For online information about Perl DBI, visit the DBI Web site, http://dbi.perl.org/.
  • For printed information, the official DBI book is Programming the Perl DBI (Alligator Descartes and Tim Bunce, O'Reilly & Associates, 2000). Information about the book is available at the DBI Web site, http://dbi.perl.org/. For information that focuses specifically on using DBI with MySQL, see MySQL and Perl for the Web (Paul DuBois, New Riders, 2001). This book's Web site is http://www.kitebird.com/mysql-perl/.

20.7 MySQL C++ API

MySQL++ is the MySQL API for C++. More information can be found at http://www.mysql.com/products/mysql++/.

20.7.1 Borland C++

You can compile the MySQL Windows source with Borland C++ 5.02. (The Windows source includes only projects for Microsoft VC++, for Borland C++ you have to do the project files yourself.)

One known problem with Borland C++ is that it uses a different structure alignment than VC++. This means that you will run into problems if you try to use the default libmysql.dll libraries (that was compiled with VC++) with Borland C++. You can do one of the following to avoid this problem.

20.8 MySQL Python API

MySQLdb provides MySQL support for Python, compliant with the Python DB API version 2.0. It can be found at http://sourceforge.net/projects/mysql-python/.

20.9 MySQL Tcl API

MySQLtcl is a simple API for accessing a MySQL database server from the Tcl programming language. It can be found at http://www.xdobry.de/mysqltcl/.

20.10 MySQL Eiffel Wrapper

Eiffel MySQL is an interface to the MySQL database server using the Eiffel programming language, written by Michael Ravits. It can be found at http://efsa.sourceforge.net/archive/ravits/mysql.htm.


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