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.
const char * name
name for portal, or NULL to let the system
select a name
SPIPlanPtr plan
prepared statement (returned by SPI_prepare)
Datum * valuesAn array of actual parameter values. Must have same length as the statement's number of arguments.
const char * nullsAn 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.
bool read_onlytrue for read-only execution
Pointer to portal containing the cursor. Note there is no error
return convention; any error will be reported via elog.