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20.8.7.3. mysql_stmt_attr_set()

my_bool mysql_stmt_attr_set(MYSQL_STMT *stmt, enum enum_stmt_attr_type option, const void *arg)

Description

Can be used to affect behavior for a prepared statement. This function may be called multiple times to set several options.

The option argument is the option that you want to set. The arg argument is the value for the option. arg should point to a variable that is set to the desired attribute value. The variable type is as indicated in the following table.

The following table shows the possible option values.

Option Argument Type Function
STMT_ATTR_UPDATE_MAX_LENGTH my_bool * If set to 1, causes mysql_stmt_store_result() to update the metadata MYSQL_FIELD->max_length value.
STMT_ATTR_CURSOR_TYPE unsigned long * Type of cursor to open for statement when mysql_stmt_execute() is invoked. *arg can be CURSOR_TYPE_NO_CURSOR (the default) or CURSOR_TYPE_READ_ONLY.
STMT_ATTR_PREFETCH_ROWS unsigned long * Number of rows to fetch from server at a time when using a cursor. *arg can be in the range from 1 to the maximum value of unsigned long. The default is 1.

Note

In MySQL 5.0, mysql_stmt_attr_get() uses unsigned int *, not my_bool *, for STMT_ATTR_UPDATE_MAX_LENGTH. This is corrected in MySQL 5.1.7.

If you use the STMT_ATTR_CURSOR_TYPE option with CURSOR_TYPE_READ_ONLY, a cursor is opened for the statement when you invoke mysql_stmt_execute(). If there is already an open cursor from a previous mysql_stmt_execute() call, it closes the cursor before opening a new one. mysql_stmt_reset() also closes any open cursor before preparing the statement for re-execution. mysql_stmt_free_result() closes any open cursor.

If you open a cursor for a prepared statement, mysql_stmt_store_result() is unnecessary, because that function causes the result set to be buffered on the client side.

The STMT_ATTR_CURSOR_TYPE option was added in MySQL 5.0.2. The STMT_ATTR_PREFETCH_ROWS option was added in MySQL 5.0.6.

Return Values

Zero if successful. Nonzero if option is unknown.

Errors

None.

Example

The following example opens a cursor for a prepared statement and sets the number of rows to fetch at a time to 5: 

MYSQL_STMT *stmt;
int rc;
unsigned long type;
unsigned long prefetch_rows = 5;

stmt = mysql_stmt_init(mysql);
type = (unsigned long) CURSOR_TYPE_READ_ONLY;
rc = mysql_stmt_attr_set(stmt, STMT_ATTR_CURSOR_TYPE, (void*) &type);
/* ... check return value ... */
rc = mysql_stmt_attr_set(stmt, STMT_ATTR_PREFETCH_ROWS,
                         (void*) &prefetch_rows);
/* ... check return value ... */