Function advance_windowaggregate_base

src/backend/executor/nodeWindowAgg.c:513–669

* advance_windowaggregate_base * Remove the oldest tuple from an aggregation. * * This is very much like advance_windowaggregate, except that we will call * the inverse transition function (which caller must have checked is * available). * * Returns true if we successfully removed the current row from this * aggregate, false if not (in the latter case, caller is responsible * for cleaning

 * for cleaning up by restarting the aggregation).
 */
static bool
advance_windowaggregate_base(WindowAggState *winstate,
							 WindowStatePerFunc perfuncstate,
							 WindowStatePerAgg peraggstate)
{
	LOCAL_FCINFO(fcinfo, FUNC_MAX_ARGS);
	WindowFuncExprState *wfuncstate = perfuncstate->wfuncstate;
	int			numArguments = perfuncstate->numArguments;
	Datum		newVal;
	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 true;
		}
	}

	/* 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 (peraggstate->invtransfn.fn_strict)
	{
		/*
		 * For a strict (inv)transfn, nothing happens when there's a NULL
		 * input; we just keep the prior transValue.  Note transValueCount
		 * doesn't change either.
		 */
		for (i = 1; i <= numArguments; i++)
		{
			if (fcinfo->args[i].isnull)
			{
				MemoryContextSwitchTo(oldContext);
				return true;
			}
		}
	}