SPI_prepare() PostgreSQL 8.1.19 Documentation SPI_prepare()NAME
SPI_prepare - prepare a plan for a command, without executing it yet
SYNOPSIS
void * SPI_prepare(const char * command, int nargs, Oid * argtypes)
DESCRIPTION
SPI_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 may
be advantageous to perform the planning only once. SPI_prepare con‐
verts 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_exe‐
cute_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 invo‐
cation of the procedure, since SPI_finish frees memory allocated for a
plan. But a plan can be saved for longer using the function SPI_save‐
plan.
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 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
There is a disadvantage to using parameters: since the planner does not
know the values that will be supplied for the parameters, it may make
worse planning choices than it would make for a normal command with all
constants visible.
2009-12-09 SPI_prepare()
