SPI_cursor_open
Synopsis
Portal SPI_cursor_open(const char * name, SPIPlanPtr plan,
Datum * values, const char * nulls,
bool read_only)
Description
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 procedure (it can, in fact, live to the end of the current transaction). Returning the portal name to the procedure'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.
Arguments
- const char * name
-
name for portal, or NULL to let the system select a name
- SPIPlanPtr plan
-
prepared statement (returned by
SPI_prepare) - Datum * values
-
An array of actual parameter values. Must have same length as the statement's number of arguments.
- const char * 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_openassumes 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_only
-
true for read-only execution
Return Value
Pointer to portal containing the cursor. Note there is no error
return convention; any error will be reported via
elog
.