Function finalize_windowaggregate

src/backend/executor/nodeWindowAgg.c:756–843

* finalize_windowaggregate * parallel to finalize_aggregate in nodeAgg.c */

 * parallel to finalize_aggregate in nodeAgg.c
 */
static void
finalize_windowaggregate(WindowAggState *winstate,
						 WindowStatePerFunc perfuncstate,
						 WindowStatePerAgg peraggstate,
						 Datum *result, bool *isnull)
{
	MemoryContext oldContext;

	/*
	 * If this is a distinct-qualified aggregate, then we have only spooled the
	 * inputs into the sorter so far. We haven't run the transition function over
	 * the input yet. Perform the sort now, and call the transition function on the
	 * unique values.
	 */
	if (peraggstate->isDistinct)
	{
		perform_distinct_windowaggregate(winstate,
										 perfuncstate,
										 peraggstate);
		/*
		 * Now we have the final transition value in peraggstate->transValue, like
		 * in the normal, non-DISTINCT, case.
		 */
	}

	oldContext = MemoryContextSwitchTo(winstate->ss.ps.ps_ExprContext->ecxt_per_tuple_memory);

	/*
	 * Apply the agg's finalfn if one is provided, else return transValue.
	 */
	if (OidIsValid(peraggstate->finalfn_oid))
	{
		LOCAL_FCINFO(fcinfo, FUNC_MAX_ARGS);
		int			numFinalArgs = peraggstate->numFinalArgs;
		bool		anynull;
		int			i;

		InitFunctionCallInfoData(fcinfodata.fcinfo, &(peraggstate->finalfn),
								 numFinalArgs,
								 perfuncstate->winCollation,
								 (void *) winstate, NULL);
		fcinfo->args[0].value =
			MakeExpandedObjectReadOnly(peraggstate->transValue,
									   peraggstate->transValueIsNull,
									   peraggstate->transtypeLen);
		fcinfo->args[0].isnull = peraggstate->transValueIsNull;
		anynull = peraggstate->transValueIsNull;

		/* Fill any remaining argument positions with nulls */
		for (i = 1; i < numFinalArgs; i++)
		{
			fcinfo->args[i].value = (Datum) 0;
			fcinfo->args[i].isnull = true;
			anynull = true;
		}

		if (fcinfo->flinfo->fn_strict && anynull)
		{