Function advance_windowaggregate

src/backend/executor/nodeWindowAgg.c:284–351

* advance_windowaggregate * parallel to advance_aggregates in nodeAgg.c */

 * parallel to advance_aggregates in nodeAgg.c
 */
static void
advance_windowaggregate(WindowAggState *winstate,
						WindowStatePerFunc perfuncstate,
						WindowStatePerAgg peraggstate)
{
	LOCAL_FCINFO(fcinfo, FUNC_MAX_ARGS);
	WindowFuncExprState *wfuncstate = perfuncstate->wfuncstate;
	ListCell   *arg;
	int			i;
	MemoryContext oldContext;
	ExprContext *econtext = winstate->tmpcontext;
	ExprState  *filter = wfuncstate->aggfilter;

	oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);

	/* Skip anything FILTERed out */
	if (filter)
	{
		bool		isnull;
		Datum		res = ExecEvalExpr(filter, econtext, &isnull);

		if (isnull || !DatumGetBool(res))
		{
			MemoryContextSwitchTo(oldContext);
			return;
		}
	}

	/* We start from 1, since the 0th arg will be the transition value */
	i = 1;
	foreach(arg, wfuncstate->args)
	{
		ExprState  *argstate = (ExprState *) lfirst(arg);

		fcinfo->args[i].value = ExecEvalExpr(argstate, econtext,
											 &fcinfo->args[i].isnull);
		i++;
	}

	/*
	 * If this is a DISTINCT-qualified aggregate, we cannot call the
	 * transition function yet. Instead, we spool the input into a tuplesort.
	 * We will perform the sort, deduplicate, and call the transition
	 * function later, after we have spooled all the input values in this
	 * partition.
	 */
	if (peraggstate->isDistinct)
	{
		Assert(list_length(wfuncstate->args) == 1);

		/*
		 * For a strict transfn, nothing happens when there's a NULL input; we
		 * just keep the prior transValue.
		 */
		if (peraggstate->transfn.fn_strict && fcinfo->args[1].isnull)
		{
			/* skip it */
		}