Function exec_for_query

src/pl/plpgsql/src/pl_exec.c:5782–5934

* exec_for_query --- execute body of FOR loop for each row from a portal * * Used by exec_stmt_fors, exec_stmt_forc and exec_stmt_dynfors */

 * Used by exec_stmt_fors, exec_stmt_forc and exec_stmt_dynfors
 */
static int
exec_for_query(PLpgSQL_execstate *estate, PLpgSQL_stmt_forq *stmt,
			   Portal portal, bool prefetch_ok)
{
	PLpgSQL_variable *var;
	SPITupleTable *tuptab;
	bool		found = false;
	int			rc = PLPGSQL_RC_OK;
	uint64		previous_id = INVALID_TUPLEDESC_IDENTIFIER;
	bool		tupdescs_match = true;
	uint64		n;

	/* Fetch loop variable's datum entry */
	var = (PLpgSQL_variable *) estate->datums[stmt->var->dno];

	/*
	 * Make sure the portal doesn't get closed by the user statements we
	 * execute.
	 */
	PinPortal(portal);

	/*
	 * In a non-atomic context, we dare not prefetch, even if it would
	 * otherwise be safe.  Aside from any semantic hazards that that might
	 * create, if we prefetch toasted data and then the user commits the
	 * transaction, the toast references could turn into dangling pointers.
	 * (Rows we haven't yet fetched from the cursor are safe, because the
	 * PersistHoldablePortal mechanism handles this scenario.)
	 */
	if (!estate->atomic)
		prefetch_ok = false;

	/*
	 * Fetch the initial tuple(s).  If prefetching is allowed then we grab a
	 * few more rows to avoid multiple trips through executor startup
	 * overhead.
	 */
	SPI_cursor_fetch(portal, true, prefetch_ok ? 10 : 1);
	tuptab = SPI_tuptable;
	n = SPI_processed;

	/*
	 * If the query didn't return any rows, set the target to NULL and fall
	 * through with found = false.
	 */
	if (n == 0)
	{
		exec_move_row(estate, var, NULL, tuptab->tupdesc);
		exec_eval_cleanup(estate);
	}
	else
		found = true;			/* processed at least one tuple */

	/*
	 * Now do the loop
	 */
	while (n > 0)
	{