Implement the FILTER clause for aggregate function calls.

This is SQL-standard with a few extensions, namely support for
subqueries and outer references in clause expressions.

catversion bump due to change in Aggref and WindowFunc.

David Fetter, reviewed by Dean Rasheed.

src/backend/executor/execQual.c

@@ -4410,6 +4410,8 @@ ExecInitExpr(Expr *node, PlanState *parent)
 
 					astate->args = (List *) ExecInitExpr((Expr *) aggref->args,
 														 parent);
+					astate->aggfilter = ExecInitExpr(aggref->aggfilter,
+													 parent);
 
 					/*
 					 * Complain if the aggregate's arguments contain any
@@ -4448,6 +4450,8 @@ ExecInitExpr(Expr *node, PlanState *parent)
 
 					wfstate->args = (List *) ExecInitExpr((Expr *) wfunc->args,
 														  parent);
+					wfstate->aggfilter = ExecInitExpr(wfunc->aggfilter,
+													  parent);
 
 					/*
 					 * Complain if the windowfunc's arguments contain any

src/backend/executor/execUtils.c

@@ -649,9 +649,9 @@ get_last_attnums(Node *node, ProjectionInfo *projInfo)
 	}
 
 	/*
-	 * Don't examine the arguments of Aggrefs or WindowFuncs, because those do
-	 * not represent expressions to be evaluated within the overall
-	 * targetlist's econtext.
+	 * Don't examine the arguments or filters of Aggrefs or WindowFuncs,
+	 * because those do not represent expressions to be evaluated within the
+	 * overall targetlist's econtext.
 	 */
 	if (IsA(node, Aggref))
 		return false;

src/backend/executor/functions.c

@@ -380,7 +380,7 @@ sql_fn_post_column_ref(ParseState *pstate, ColumnRef *cref, Node *var)
 		param = ParseFuncOrColumn(pstate,
 								  list_make1(subfield),
 								  list_make1(param),
-								  NIL, false, false, false,
+								  NIL, NULL, false, false, false,
 								  NULL, true, cref->location);
 	}
 

src/backend/executor/nodeAgg.c

@@ -484,10 +484,23 @@ advance_aggregates(AggState *aggstate, AggStatePerGroup pergroup)
 	{
 		AggStatePerAgg peraggstate = &aggstate->peragg[aggno];
 		AggStatePerGroup pergroupstate = &pergroup[aggno];
+		ExprState  *filter = peraggstate->aggrefstate->aggfilter;
 		int			nargs = peraggstate->numArguments;
 		int			i;
 		TupleTableSlot *slot;
 
+		/* Skip anything FILTERed out */
+		if (filter)
+		{
+			bool		isnull;
+			Datum		res;
+
+			res = ExecEvalExprSwitchContext(filter, aggstate->tmpcontext,
+											&isnull, NULL);
+			if (isnull || !DatumGetBool(res))
+				continue;
+		}
+
 		/* Evaluate the current input expressions for this aggregate */
 		slot = ExecProject(peraggstate->evalproj, NULL);
 

src/backend/executor/nodeWindowAgg.c

@@ -227,9 +227,23 @@ advance_windowaggregate(WindowAggState *winstate,
 	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, NULL);
+
+		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)