Function ExecWindowAgg

src/backend/executor/nodeWindowAgg.c:2394–2594

----------------- * ExecWindowAgg * * ExecWindowAgg receives tuples from its outer subplan and * stores them into a tuplestore, then processes window functions. * This node doesn't reduce nor qualify any row so the number of * returned rows is exactly the same as its outer subplan's result. * ----------------- */

 * -----------------
 */
static TupleTableSlot *
ExecWindowAgg(PlanState *pstate)
{
	WindowAggState *winstate = castNode(WindowAggState, pstate);
	ExprContext *econtext;
	int			i;
	int			numfuncs;

	CHECK_FOR_INTERRUPTS();

	if (winstate->all_done)
		return NULL;

	/*
	 * Compute frame offset values, if any, during first call (or after a
	 * rescan).  These are assumed to hold constant throughout the scan; if
	 * user gives us a volatile expression, we'll only use its initial value.
	 *
	 * GPDB: We accept non-constant frame offsets, too. If they're not
	 * constants, we'll compute them later.
	 */
	if (winstate->all_first &&
		winstate->start_offset_var_free &&
		winstate->end_offset_var_free)
	{
		compute_start_end_offsets(winstate);

		winstate->all_first = false;
	}

	if (winstate->buffer == NULL)
	{
		/* Initialize for first partition and set current row = 0 */
		begin_partition(winstate);
		/* If there are no input rows, we'll detect that and exit below */
	}
	else
	{
		/* Advance current row within partition */
		winstate->currentpos++;
		/* This might mean that the frame moves, too */
		winstate->framehead_valid = false;
		winstate->frametail_valid = false;
		/* we don't need to invalidate grouptail here; see below */

		if (!winstate->start_offset_var_free)
			winstate->start_offset_valid = false;
		if (!winstate->end_offset_var_free)
			winstate->end_offset_valid = false;
	}

	/*
	 * Spool all tuples up to and including the current row, if we haven't
	 * already
	 */
	spool_tuples(winstate, winstate->currentpos);

#ifdef FAULT_INJECTOR