SPI_prepare — prepare a plan for a command, without executing it yet
void * SPI_prepare(const char *command
, intnargs
, Oid *argtypes
)
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
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
.
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
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
.