SPI_cursor_open
— set up a cursor using a statement created with SPI_prepare
Portal SPI_cursor_open(const char *name
, SPIPlanPtrplan
, Datum *values
, const char *nulls
, boolread_only
)
SPI_cursor_open
sets up a cursor (internally,
a portal) that will execute a statement prepared by
SPI_prepare
. The parameters have the same
meanings as the corresponding parameters to
SPI_execute_plan
.
Using a cursor instead of executing the statement directly has two benefits. First, the result rows can be retrieved a few at a time, avoiding memory overrun for queries that return many rows. Second, a portal can outlive the current C function (it can, in fact, live to the end of the current transaction). Returning the portal name to the C function's caller provides a way of returning a row set as result.
The passed-in parameter data will be copied into the cursor's portal, so it can be freed while the cursor still exists.
name
name for portal, or NULL
to let the system
select a name
plan
prepared statement (returned by SPI_prepare
)
values
An array of actual parameter values. Must have same length as the statement's number of arguments.
nulls
An array describing which parameters are null. Must have same length as the statement's number of arguments.
If nulls
is NULL
then
SPI_cursor_open
assumes that no parameters
are null. Otherwise, each entry of the nulls
array should be ' '
if the corresponding parameter
value is non-null, or 'n'
if the corresponding parameter
value is null. (In the latter case, the actual value in the
corresponding values
entry doesn't matter.) Note
that nulls
is not a text string, just an array:
it does not need a '\0'
terminator.
read_only
true
for read-only execution
Pointer to portal containing the cursor. Note there is no error
return convention; any error will be reported via elog
.