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
When the same or a similar command is to be executed
repeatedly, it may be advantageous to perform the planning only
SPI_prepare converts a
command string into an execution plan that can be executed
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
can be used only in the current invocation of the procedure,
SPI_finish frees memory
allocated for a plan. But a plan can be saved for longer using
number of input parameters ($1, $2, etc.)
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
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.
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.
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