SPI_PREPARE(3) PostgreSQL 9.1.9 Documentation SPI_PREPARE(3)NAMESPI_prepare - prepare a plan for a command, without executing it yet
SYNOPSIS
SPIPlanPtr SPI_prepare(const char * command, int nargs, Oid * argtypes)
DESCRIPTIONSPI_prepare creates and returns an execution plan for the specified
command, but doesn't execute the command. This function should only be
called from a connected procedure.
When the same or a similar command is to be executed repeatedly, it
might be advantageous to perform the planning only once. SPI_prepare
converts a command string into an execution plan that can be executed
repeatedly using SPI_execute_plan.
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 plan returned by SPI_prepare can be used only in the current
invocation of the procedure, since SPI_finish frees memory allocated
for a plan. But a plan can be saved for longer using the function
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 VALUESPI_prepare returns a non-null pointer to an execution plan. 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
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.
There is a disadvantage to using parameters: since the planner does not
know the values that will be supplied for the parameters, it might make
worse planning choices than it would make for a normal command with all
constants visible.
PostgreSQL 9.1.9 2013-04-01 SPI_PREPARE(3)
