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_execp 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 since
SPI_finish frees memory allocated
for a plan. But a plan can be saved for longer using the function
number of input parameters ($1, $2, etc.)
pointer to an array containing the OIDs of the data types of the parameters
SPI_prepare returns non-null
pointer to an execution plan. On error, NULL will be returned. In both cases, SPI_result will be set analogous to the value
SPI_exec, 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.
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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