SPI_PREPARE(3)						  PostgreSQL 9.2.7 Documentation					    SPI_PREPARE(3)

NAME

       SPI_prepare - prepare a statement, without executing it yet

SYNOPSIS

       SPIPlanPtr SPI_prepare(const char * command, int nargs, Oid * argtypes)

DESCRIPTION

       SPI_prepare creates and returns a prepared statement for the specified command, but doesn't execute the command. The prepared statement can
       later be executed repeatedly using SPI_execute_plan.

       When the same or a similar command is to be executed repeatedly, it is generally advantageous to perform parse analysis only once, and
       might furthermore be advantageous to re-use an execution plan for the command.  SPI_prepare converts a command string into a prepared
       statement that encapsulates the results of parse analysis. The prepared statement also provides a place for caching an execution plan if it
       is found that generating a custom plan for each execution is not helpful.

       A prepared command can be generalized by writing parameters ($1, $2, etc.) in place of what would be constants in a normal command. The
       actual values of the parameters are then specified when SPI_execute_plan is called. This allows the prepared command to be used over a
       wider range of situations than would be possible without parameters.

       The statement returned by SPI_prepare can be used only in the current invocation of the procedure, since SPI_finish frees memory allocated
       for such a statement. But the statement can be saved for longer using the functions SPI_keepplan or SPI_saveplan.

ARGUMENTS

       const char * command
	   command string

       int nargs
	   number of input parameters ($1, $2, etc.)

       Oid * argtypes
	   pointer to an array containing the OIDs of the data types of the parameters

RETURN VALUE

       SPI_prepare returns a non-null pointer to an SPIPlan, which is an opaque struct representing a prepared statement. On error, NULL will be
       returned, and SPI_result will be set to one of the same error codes used by SPI_execute, except that it is set to SPI_ERROR_ARGUMENT if
       command is NULL, or if nargs is less than 0, or if nargs is greater than 0 and argtypes is NULL.

NOTES

       If no parameters are defined, a generic plan will be created at the first use of SPI_execute_plan, and used for all subsequent executions
       as well. If there are parameters, the first few uses of SPI_execute_plan will generate custom plans that are specific to the supplied
       parameter values. After enough uses of the same prepared statement, SPI_execute_plan will build a generic plan, and if that is not too much
       more expensive than the custom plans, it will start using the generic plan instead of re-planning each time. If this default behavior is
       unsuitable, you can alter it by passing the CURSOR_OPT_GENERIC_PLAN or CURSOR_OPT_CUSTOM_PLAN flag to SPI_prepare_cursor, to force use of
       generic or custom plans respectively.

       This function should only be called from a connected procedure.

       SPIPlanPtr is declared as a pointer to an opaque struct type in spi.h. It is unwise to try to access its contents directly, as that makes
       your code much more likely to break in future revisions of PostgreSQL.

       The name SPIPlanPtr is somewhat historical, since the data structure no longer necessarily contains an execution plan.

PostgreSQL 9.2.7						    2014-02-17							    SPI_PREPARE(3)