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.

contrib/pg_stat_statements/pg_stat_statements.c

@@ -1546,6 +1546,7 @@ JumbleExpr(pgssJumbleState *jstate, Node *node)
 				JumbleExpr(jstate, (Node *) expr->args);
 				JumbleExpr(jstate, (Node *) expr->aggorder);
 				JumbleExpr(jstate, (Node *) expr->aggdistinct);
+				JumbleExpr(jstate, (Node *) expr->aggfilter);
 			}
 			break;
 		case T_WindowFunc:
@@ -1555,6 +1556,7 @@ JumbleExpr(pgssJumbleState *jstate, Node *node)
 				APP_JUMB(expr->winfnoid);
 				APP_JUMB(expr->winref);
 				JumbleExpr(jstate, (Node *) expr->args);
+				JumbleExpr(jstate, (Node *) expr->aggfilter);
 			}
 			break;
 		case T_ArrayRef:

doc/src/sgml/keywords.sgml

@@ -1786,7 +1786,7 @@
    </row>
    <row>
     <entry><token>FILTER</token></entry>
-    <entry></entry>
+    <entry>non-reserved</entry>
     <entry>reserved</entry>
     <entry>reserved</entry>
     <entry></entry>

doc/src/sgml/ref/select.sgml

@@ -598,6 +598,11 @@ GROUP BY <replaceable class="parameter">expression</replaceable> [, ...]
     making up each group, producing a separate value for each group
     (whereas without <literal>GROUP BY</literal>, an aggregate
     produces a single value computed across all the selected rows).
+    The set of rows fed to the aggregate function can be further filtered by
+    attaching a <literal>FILTER</literal> clause to the aggregate function
+    call; see <xref linkend="syntax-aggregates"> for more information.  When
+    a <literal>FILTER</literal> clause is present, only those rows matching it
+    are included.
     When <literal>GROUP BY</literal> is present, it is not valid for
     the <command>SELECT</command> list expressions to refer to
     ungrouped columns except within aggregate functions or if the

doc/src/sgml/syntax.sgml

@@ -1554,6 +1554,10 @@ sqrt(2)
     <secondary>invocation</secondary>
    </indexterm>
 
+   <indexterm zone="syntax-aggregates">
+    <primary>filter</primary>
+   </indexterm>
+
    <para>
     An <firstterm>aggregate expression</firstterm> represents the
     application of an aggregate function across the rows selected by a
@@ -1562,19 +1566,19 @@ sqrt(2)
     syntax of an aggregate expression is one of the following:
 
 <synopsis>
-<replaceable>aggregate_name</replaceable> (<replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] )
-<replaceable>aggregate_name</replaceable> (ALL <replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] )
-<replaceable>aggregate_name</replaceable> (DISTINCT <replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] )
-<replaceable>aggregate_name</replaceable> ( * )
+<replaceable>aggregate_name</replaceable> (<replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
+<replaceable>aggregate_name</replaceable> (ALL <replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
+<replaceable>aggregate_name</replaceable> (DISTINCT <replaceable>expression</replaceable> [ , ... ] [ <replaceable>order_by_clause</replaceable> ] ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
+<replaceable>aggregate_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ]
 </synopsis>
 
     where <replaceable>aggregate_name</replaceable> is a previously
-    defined aggregate (possibly qualified with a schema name),
+    defined aggregate (possibly qualified with a schema name) and
     <replaceable>expression</replaceable> is
     any value expression that does not itself contain an aggregate
-    expression or a window function call, and
-    <replaceable>order_by_clause</replaceable> is a optional
-    <literal>ORDER BY</> clause as described below.
+    expression or a window function call.  The optional
+    <replaceable>order_by_clause</replaceable> and
+    <replaceable>filter_clause</replaceable> are described below.
    </para>
 
    <para>
@@ -1606,6 +1610,23 @@ sqrt(2)
     distinct non-null values of <literal>f1</literal>.
    </para>
 
+   <para>
+    If <literal>FILTER</literal> is specified, then only the input
+    rows for which the <replaceable>filter_clause</replaceable>
+    evaluates to true are fed to the aggregate function; other rows
+    are discarded.  For example:
+<programlisting>
+SELECT
+    count(*) AS unfiltered,
+    count(*) FILTER (WHERE i < 5) AS filtered
+FROM generate_series(1,10) AS s(i);
+ unfiltered | filtered 
+------------+----------
+         10 |        4
+(1 row)
+</programlisting>
+   </para>
+
    <para>
     Ordinarily, the input rows are fed to the aggregate function in an
     unspecified order.  In many cases this does not matter; for example,
@@ -1709,10 +1730,10 @@ SELECT string_agg(a ORDER BY a, ',') FROM table;  -- incorrect
     The syntax of a window function call is one of the following:
 
 <synopsis>
-<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) OVER ( <replaceable class="parameter">window_definition</replaceable> )
-<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) OVER <replaceable>window_name</replaceable>
-<replaceable>function_name</replaceable> ( * ) OVER ( <replaceable class="parameter">window_definition</replaceable> )
-<replaceable>function_name</replaceable> ( * ) OVER <replaceable>window_name</replaceable>
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
+<replaceable>function_name</replaceable> (<optional><replaceable>expression</replaceable> <optional>, <replaceable>expression</replaceable> ... </optional></optional>) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
+<replaceable>function_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER ( <replaceable class="parameter">window_definition</replaceable> )
+<replaceable>function_name</replaceable> ( * ) [ FILTER ( WHERE <replaceable>filter_clause</replaceable> ) ] OVER <replaceable>window_name</replaceable>
 </synopsis>
     where <replaceable class="parameter">window_definition</replaceable>
     has the syntax
@@ -1836,7 +1857,8 @@ UNBOUNDED FOLLOWING
     The built-in window functions are described in <xref
     linkend="functions-window-table">.  Other window functions can be added by
     the user.  Also, any built-in or user-defined aggregate function can be
-    used as a window function.
+    used as a window function.  Only aggregate window functions accept
+    a <literal>FILTER</literal> clause.
    </para>
 
    <para>

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)

src/backend/nodes/copyfuncs.c

@@ -1137,6 +1137,7 @@ _copyAggref(const Aggref *from)
 	COPY_NODE_FIELD(args);
 	COPY_NODE_FIELD(aggorder);
 	COPY_NODE_FIELD(aggdistinct);
+	COPY_NODE_FIELD(aggfilter);
 	COPY_SCALAR_FIELD(aggstar);
 	COPY_SCALAR_FIELD(agglevelsup);
 	COPY_LOCATION_FIELD(location);
@@ -1157,6 +1158,7 @@ _copyWindowFunc(const WindowFunc *from)
 	COPY_SCALAR_FIELD(wincollid);
 	COPY_SCALAR_FIELD(inputcollid);
 	COPY_NODE_FIELD(args);
+	COPY_NODE_FIELD(aggfilter);
 	COPY_SCALAR_FIELD(winref);
 	COPY_SCALAR_FIELD(winstar);
 	COPY_SCALAR_FIELD(winagg);
@@ -2152,6 +2154,7 @@ _copyFuncCall(const FuncCall *from)
 	COPY_NODE_FIELD(funcname);
 	COPY_NODE_FIELD(args);
 	COPY_NODE_FIELD(agg_order);
+	COPY_NODE_FIELD(agg_filter);
 	COPY_SCALAR_FIELD(agg_star);
 	COPY_SCALAR_FIELD(agg_distinct);
 	COPY_SCALAR_FIELD(func_variadic);

src/backend/nodes/equalfuncs.c

@@ -196,6 +196,7 @@ _equalAggref(const Aggref *a, const Aggref *b)
 	COMPARE_NODE_FIELD(args);
 	COMPARE_NODE_FIELD(aggorder);
 	COMPARE_NODE_FIELD(aggdistinct);
+	COMPARE_NODE_FIELD(aggfilter);
 	COMPARE_SCALAR_FIELD(aggstar);
 	COMPARE_SCALAR_FIELD(agglevelsup);
 	COMPARE_LOCATION_FIELD(location);
@@ -211,6 +212,7 @@ _equalWindowFunc(const WindowFunc *a, const WindowFunc *b)
 	COMPARE_SCALAR_FIELD(wincollid);
 	COMPARE_SCALAR_FIELD(inputcollid);
 	COMPARE_NODE_FIELD(args);
+	COMPARE_NODE_FIELD(aggfilter);
 	COMPARE_SCALAR_FIELD(winref);
 	COMPARE_SCALAR_FIELD(winstar);
 	COMPARE_SCALAR_FIELD(winagg);
@@ -1993,6 +1995,7 @@ _equalFuncCall(const FuncCall *a, const FuncCall *b)
 	COMPARE_NODE_FIELD(funcname);
 	COMPARE_NODE_FIELD(args);
 	COMPARE_NODE_FIELD(agg_order);
+	COMPARE_NODE_FIELD(agg_filter);
 	COMPARE_SCALAR_FIELD(agg_star);
 	COMPARE_SCALAR_FIELD(agg_distinct);
 	COMPARE_SCALAR_FIELD(func_variadic);

src/backend/nodes/makefuncs.c

@@ -526,6 +526,7 @@ makeFuncCall(List *name, List *args, int location)
 	n->args = args;
 	n->location = location;
 	n->agg_order = NIL;
+	n->agg_filter = NULL;
 	n->agg_star = FALSE;
 	n->agg_distinct = FALSE;
 	n->func_variadic = FALSE;

src/backend/nodes/nodeFuncs.c

@@ -1570,6 +1570,8 @@ expression_tree_walker(Node *node,
 				if (expression_tree_walker((Node *) expr->aggdistinct,
 										   walker, context))
 					return true;
+				if (walker((Node *) expr->aggfilter, context))
+					return true;
 			}
 			break;
 		case T_WindowFunc:
@@ -1580,6 +1582,8 @@ expression_tree_walker(Node *node,
 				if (expression_tree_walker((Node *) expr->args,
 										   walker, context))
 					return true;
+				if (walker((Node *) expr->aggfilter, context))
+					return true;
 			}
 			break;
 		case T_ArrayRef:
@@ -2079,6 +2083,7 @@ expression_tree_mutator(Node *node,
 				MUTATE(newnode->args, aggref->args, List *);
 				MUTATE(newnode->aggorder, aggref->aggorder, List *);
 				MUTATE(newnode->aggdistinct, aggref->aggdistinct, List *);
+				MUTATE(newnode->aggfilter, aggref->aggfilter, Expr *);
 				return (Node *) newnode;
 			}
 			break;
@@ -2089,6 +2094,7 @@ expression_tree_mutator(Node *node,
 
 				FLATCOPY(newnode, wfunc, WindowFunc);
 				MUTATE(newnode->args, wfunc->args, List *);
+				MUTATE(newnode->aggfilter, wfunc->aggfilter, Expr *);
 				return (Node *) newnode;
 			}
 			break;
@@ -2951,6 +2957,8 @@ raw_expression_tree_walker(Node *node,
 					return true;
 				if (walker(fcall->agg_order, context))
 					return true;
+				if (walker(fcall->agg_filter, context))
+					return true;
 				if (walker(fcall->over, context))
 					return true;
 				/* function name is deemed uninteresting */

src/backend/nodes/outfuncs.c

@@ -958,6 +958,7 @@ _outAggref(StringInfo str, const Aggref *node)
 	WRITE_NODE_FIELD(args);
 	WRITE_NODE_FIELD(aggorder);
 	WRITE_NODE_FIELD(aggdistinct);
+	WRITE_NODE_FIELD(aggfilter);
 	WRITE_BOOL_FIELD(aggstar);
 	WRITE_UINT_FIELD(agglevelsup);
 	WRITE_LOCATION_FIELD(location);
@@ -973,6 +974,7 @@ _outWindowFunc(StringInfo str, const WindowFunc *node)
 	WRITE_OID_FIELD(wincollid);
 	WRITE_OID_FIELD(inputcollid);
 	WRITE_NODE_FIELD(args);
+	WRITE_NODE_FIELD(aggfilter);
 	WRITE_UINT_FIELD(winref);
 	WRITE_BOOL_FIELD(winstar);
 	WRITE_BOOL_FIELD(winagg);
@@ -2080,6 +2082,7 @@ _outFuncCall(StringInfo str, const FuncCall *node)
 	WRITE_NODE_FIELD(funcname);
 	WRITE_NODE_FIELD(args);
 	WRITE_NODE_FIELD(agg_order);
+	WRITE_NODE_FIELD(agg_filter);
 	WRITE_BOOL_FIELD(agg_star);
 	WRITE_BOOL_FIELD(agg_distinct);
 	WRITE_BOOL_FIELD(func_variadic);

src/backend/nodes/readfuncs.c

@@ -479,6 +479,7 @@ _readAggref(void)
 	READ_NODE_FIELD(args);
 	READ_NODE_FIELD(aggorder);
 	READ_NODE_FIELD(aggdistinct);
+	READ_NODE_FIELD(aggfilter);
 	READ_BOOL_FIELD(aggstar);
 	READ_UINT_FIELD(agglevelsup);
 	READ_LOCATION_FIELD(location);
@@ -499,6 +500,7 @@ _readWindowFunc(void)
 	READ_OID_FIELD(wincollid);
 	READ_OID_FIELD(inputcollid);
 	READ_NODE_FIELD(args);
+	READ_NODE_FIELD(aggfilter);
 	READ_UINT_FIELD(winref);
 	READ_BOOL_FIELD(winstar);
 	READ_BOOL_FIELD(winagg);

src/backend/optimizer/path/costsize.c

@@ -1590,6 +1590,14 @@ cost_windowagg(Path *path, PlannerInfo *root,
 		startup_cost += argcosts.startup;
 		wfunccost += argcosts.per_tuple;
 
+		/*
+		 * Add the filter's cost to per-input-row costs.  XXX We should reduce
+		 * input expression costs according to filter selectivity.
+		 */
+		cost_qual_eval_node(&argcosts, (Node *) wfunc->aggfilter, root);
+		startup_cost += argcosts.startup;
+		wfunccost += argcosts.per_tuple;
+
 		total_cost += wfunccost * input_tuples;
 	}
 

src/backend/optimizer/plan/planagg.c

@@ -329,6 +329,12 @@ find_minmax_aggs_walker(Node *node, List **context)
 		 */
 		if (aggref->aggorder != NIL)
 			return true;
+		/*
+		 * We might implement the optimization when a FILTER clause is present
+		 * by adding the filter to the quals of the generated subquery.
+		 */
+		if (aggref->aggfilter != NULL)
+			return true;
 		/* note: we do not care if DISTINCT is mentioned ... */
 
 		aggsortop = fetch_agg_sort_op(aggref->aggfnoid);

src/backend/optimizer/util/clauses.c

@@ -495,6 +495,15 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
 		costs->transCost.startup += argcosts.startup;
 		costs->transCost.per_tuple += argcosts.per_tuple;
 
+		/*
+		 * Add the filter's cost to per-input-row costs.  XXX We should reduce
+		 * input expression costs according to filter selectivity.
+		 */
+		cost_qual_eval_node(&argcosts, (Node *) aggref->aggfilter,
+							context->root);
+		costs->transCost.startup += argcosts.startup;
+		costs->transCost.per_tuple += argcosts.per_tuple;
+
 		/* extract argument types (ignoring any ORDER BY expressions) */
 		inputTypes = (Oid *) palloc(sizeof(Oid) * list_length(aggref->args));
 		numArguments = 0;
@@ -565,7 +574,8 @@ count_agg_clauses_walker(Node *node, count_agg_clauses_context *context)
 
 		/*
 		 * Complain if the aggregate's arguments contain any aggregates;
-		 * nested agg functions are semantically nonsensical.
+		 * nested agg functions are semantically nonsensical.  Aggregates in
+		 * the FILTER clause are detected in transformAggregateCall().
 		 */
 		if (contain_agg_clause((Node *) aggref->args))
 			ereport(ERROR,
@@ -639,7 +649,8 @@ find_window_functions_walker(Node *node, WindowFuncLists *lists)
 
 		/*
 		 * Complain if the window function's arguments contain window
-		 * functions
+		 * functions.  Window functions in the FILTER clause are detected in
+		 * transformAggregateCall().
 		 */
 		if (contain_window_function((Node *) wfunc->args))
 			ereport(ERROR,

src/backend/parser/gram.y

@@ -492,6 +492,7 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 				opt_frame_clause frame_extent frame_bound
 %type <str>		opt_existing_window_name
 %type <boolean> opt_if_not_exists
+%type <node>    filter_clause
 
 /*
  * Non-keyword token types.  These are hard-wired into the "flex" lexer.
@@ -538,8 +539,8 @@ static Node *makeRecursiveViewSelect(char *relname, List *aliases, Node *query);
 	EXCLUDE EXCLUDING EXCLUSIVE EXECUTE EXISTS EXPLAIN
 	EXTENSION EXTERNAL EXTRACT
 
-	FALSE_P FAMILY FETCH FIRST_P FLOAT_P FOLLOWING FOR FORCE FOREIGN FORWARD
-	FREEZE FROM FULL FUNCTION FUNCTIONS
+	FALSE_P FAMILY FETCH FILTER FIRST_P FLOAT_P FOLLOWING FOR
+	FORCE FOREIGN FORWARD FREEZE FROM FULL FUNCTION FUNCTIONS
 
 	GLOBAL GRANT GRANTED GREATEST GROUP_P
 
@@ -11112,10 +11113,11 @@ func_application: func_name '(' ')'
  * (Note that many of the special SQL functions wouldn't actually make any
  * sense as functional index entries, but we ignore that consideration here.)
  */
-func_expr: func_application over_clause 
+func_expr: func_application filter_clause over_clause 
 				{
               		FuncCall *n = (FuncCall*)$1;
-					n->over = $2;
+					n->agg_filter = $2;
+					n->over = $3;
 					$$ = (Node*)n;
 				} 
 			| func_expr_common_subexpr
@@ -11526,6 +11528,11 @@ window_definition:
 				}
 		;
 
+filter_clause:
+             FILTER '(' WHERE a_expr ')'            { $$ = $4; }
+             | /*EMPTY*/                            { $$ = NULL; }
+         ;
+
 over_clause: OVER window_specification
 				{ $$ = $2; }
 			| OVER ColId
@@ -12500,6 +12507,7 @@ unreserved_keyword:
 			| EXTENSION
 			| EXTERNAL
 			| FAMILY
+			| FILTER
 			| FIRST_P
 			| FOLLOWING
 			| FORCE

src/backend/parser/parse_agg.c

@@ -44,7 +44,7 @@ typedef struct
 	int			sublevels_up;
 } check_ungrouped_columns_context;
 
-static int	check_agg_arguments(ParseState *pstate, List *args);
+static int	check_agg_arguments(ParseState *pstate, List *args, Expr *filter);
 static bool check_agg_arguments_walker(Node *node,
 						   check_agg_arguments_context *context);
 static void check_ungrouped_columns(Node *node, ParseState *pstate, Query *qry,
@@ -160,7 +160,7 @@ transformAggregateCall(ParseState *pstate, Aggref *agg,
 	 * Check the arguments to compute the aggregate's level and detect
 	 * improper nesting.
 	 */
-	min_varlevel = check_agg_arguments(pstate, agg->args);
+	min_varlevel = check_agg_arguments(pstate, agg->args, agg->aggfilter);
 	agg->agglevelsup = min_varlevel;
 
 	/* Mark the correct pstate level as having aggregates */
@@ -207,6 +207,9 @@ transformAggregateCall(ParseState *pstate, Aggref *agg,
 		case EXPR_KIND_HAVING:
 			/* okay */
 			break;
+		case EXPR_KIND_FILTER:
+			errkind = true;
+			break;
 		case EXPR_KIND_WINDOW_PARTITION:
 			/* okay */
 			break;
@@ -299,8 +302,8 @@ transformAggregateCall(ParseState *pstate, Aggref *agg,
  *	  one is its parent, etc).
  *
  * The aggregate's level is the same as the level of the lowest-level variable
- * or aggregate in its arguments; or if it contains no variables at all, we
- * presume it to be local.
+ * or aggregate in its arguments or filter expression; or if it contains no
+ * variables at all, we presume it to be local.
  *
  * We also take this opportunity to detect any aggregates or window functions
  * nested within the arguments.  We can throw error immediately if we find
@@ -309,7 +312,7 @@ transformAggregateCall(ParseState *pstate, Aggref *agg,
  * which we can't know until we finish scanning the arguments.
  */
 static int
-check_agg_arguments(ParseState *pstate, List *args)
+check_agg_arguments(ParseState *pstate, List *args, Expr *filter)
 {
 	int			agglevel;
 	check_agg_arguments_context context;
@@ -323,6 +326,10 @@ check_agg_arguments(ParseState *pstate, List *args)
 								  check_agg_arguments_walker,
 								  (void *) &context);
 
+	(void) expression_tree_walker((Node *) filter,
+								  check_agg_arguments_walker,
+								  (void *) &context);
+
 	/*
 	 * If we found no vars nor aggs at all, it's a level-zero aggregate;
 	 * otherwise, its level is the minimum of vars or aggs.
@@ -481,6 +488,9 @@ transformWindowFuncCall(ParseState *pstate, WindowFunc *wfunc,
 		case EXPR_KIND_HAVING:
 			errkind = true;
 			break;
+		case EXPR_KIND_FILTER:
+			errkind = true;
+			break;
 		case EXPR_KIND_WINDOW_PARTITION:
 		case EXPR_KIND_WINDOW_ORDER:
 		case EXPR_KIND_WINDOW_FRAME_RANGE:
@@ -807,11 +817,10 @@ check_ungrouped_columns_walker(Node *node,
 
 	/*
 	 * If we find an aggregate call of the original level, do not recurse into
-	 * its arguments; ungrouped vars in the arguments are not an error. We can
-	 * also skip looking at the arguments of aggregates of higher levels,
-	 * since they could not possibly contain Vars that are of concern to us
-	 * (see transformAggregateCall).  We do need to look into the arguments of
-	 * aggregates of lower levels, however.
+	 * its arguments or filter; ungrouped vars there are not an error. We can
+	 * also skip looking at aggregates of higher levels, since they could not
+	 * possibly contain Vars of concern to us (see transformAggregateCall).
+	 * We do need to look at aggregates of lower levels, however.
 	 */
 	if (IsA(node, Aggref) &&
 		(int) ((Aggref *) node)->agglevelsup >= context->sublevels_up)

src/backend/parser/parse_collate.c

@@ -575,6 +575,10 @@ assign_collations_walker(Node *node, assign_collations_context *context)
 							 * the case above for T_TargetEntry will apply
 							 * appropriate checks to agg ORDER BY items.
 							 *
+							 * Likewise, we assign collations for the (bool)
+							 * expression in aggfilter, independently of any
+							 * other args.
+							 *
 							 * We need not recurse into the aggorder or
 							 * aggdistinct lists, because those contain only
 							 * SortGroupClause nodes which we need not
@@ -595,6 +599,24 @@ assign_collations_walker(Node *node, assign_collations_context *context)
 									(void) assign_collations_walker((Node *) tle,
 																&loccontext);
 							}
+
+							assign_expr_collations(context->pstate,
+												 (Node *) aggref->aggfilter);
+						}
+						break;
+					case T_WindowFunc:
+						{
+							/*
+							 * WindowFunc requires special processing only for
+							 * its aggfilter clause, as for aggregates.
+							 */
+							WindowFunc *wfunc = (WindowFunc *) node;
+
+							(void) assign_collations_walker((Node *) wfunc->args,
+															&loccontext);
+
+							assign_expr_collations(context->pstate,
+												   (Node *) wfunc->aggfilter);
 						}
 						break;
 					case T_CaseExpr:

src/backend/parser/parse_expr.c

@@ -22,6 +22,7 @@
 #include "nodes/nodeFuncs.h"
 #include "optimizer/var.h"
 #include "parser/analyze.h"
+#include "parser/parse_clause.h"
 #include "parser/parse_coerce.h"
 #include "parser/parse_collate.h"
 #include "parser/parse_expr.h"
@@ -462,7 +463,7 @@ transformIndirection(ParseState *pstate, Node *basenode, List *indirection)
 			newresult = ParseFuncOrColumn(pstate,
 										  list_make1(n),
 										  list_make1(result),
-										  NIL, false, false, false,
+										  NIL, NULL, false, false, false,
 										  NULL, true, location);
 			if (newresult == NULL)
 				unknown_attribute(pstate, result, strVal(n), location);
@@ -630,7 +631,7 @@ transformColumnRef(ParseState *pstate, ColumnRef *cref)
 					node = ParseFuncOrColumn(pstate,
 											 list_make1(makeString(colname)),
 											 list_make1(node),
-											 NIL, false, false, false,
+											 NIL, NULL, false, false, false,
 											 NULL, true, cref->location);
 				}
 				break;
@@ -675,7 +676,7 @@ transformColumnRef(ParseState *pstate, ColumnRef *cref)
 					node = ParseFuncOrColumn(pstate,
 											 list_make1(makeString(colname)),
 											 list_make1(node),
-											 NIL, false, false, false,
+											 NIL, NULL, false, false, false,
 											 NULL, true, cref->location);
 				}
 				break;
@@ -733,7 +734,7 @@ transformColumnRef(ParseState *pstate, ColumnRef *cref)
 					node = ParseFuncOrColumn(pstate,
 											 list_make1(makeString(colname)),
 											 list_make1(node),
-											 NIL, false, false, false,
+											 NIL, NULL, false, false, false,
 											 NULL, true, cref->location);
 				}
 				break;
@@ -1241,6 +1242,7 @@ transformFuncCall(ParseState *pstate, FuncCall *fn)
 {
 	List	   *targs;
 	ListCell   *args;
+	Expr	   *tagg_filter;
 
 	/* Transform the list of arguments ... */
 	targs = NIL;
@@ -1250,11 +1252,22 @@ transformFuncCall(ParseState *pstate, FuncCall *fn)
 													(Node *) lfirst(args)));
 	}
 
+	/*
+	 * Transform the aggregate filter using transformWhereClause(), to which
+	 * FILTER is virtually identical...
+	 */
+	tagg_filter = NULL;
+	if (fn->agg_filter != NULL)
+		tagg_filter = (Expr *)
+			transformWhereClause(pstate, (Node *) fn->agg_filter,
+								 EXPR_KIND_FILTER, "FILTER");
+
 	/* ... and hand off to ParseFuncOrColumn */
 	return ParseFuncOrColumn(pstate,
 							 fn->funcname,
 							 targs,
 							 fn->agg_order,
+							 tagg_filter,
 							 fn->agg_star,
 							 fn->agg_distinct,
 							 fn->func_variadic,
@@ -1430,6 +1443,7 @@ transformSubLink(ParseState *pstate, SubLink *sublink)
 		case EXPR_KIND_FROM_FUNCTION:
 		case EXPR_KIND_WHERE:
 		case EXPR_KIND_HAVING:
+		case EXPR_KIND_FILTER:
 		case EXPR_KIND_WINDOW_PARTITION:
 		case EXPR_KIND_WINDOW_ORDER:
 		case EXPR_KIND_WINDOW_FRAME_RANGE:
@@ -2579,6 +2593,8 @@ ParseExprKindName(ParseExprKind exprKind)
 			return "WHERE";
 		case EXPR_KIND_HAVING:
 			return "HAVING";
+		case EXPR_KIND_FILTER:
+			return "FILTER";
 		case EXPR_KIND_WINDOW_PARTITION:
 			return "window PARTITION BY";
 		case EXPR_KIND_WINDOW_ORDER:

src/backend/parser/parse_func.c

@@ -56,13 +56,13 @@ static Node *ParseComplexProjection(ParseState *pstate, char *funcname,
  *	Also, when is_column is true, we return NULL on failure rather than
  *	reporting a no-such-function error.
  *
- *	The argument expressions (in fargs) must have been transformed already.
- *	But the agg_order expressions, if any, have not been.
+ *	The argument expressions (in fargs) and filter must have been transformed
+ *	already.  But the agg_order expressions, if any, have not been.
  */
 Node *
 ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
-				  List *agg_order, bool agg_star, bool agg_distinct,
-				  bool func_variadic,
+				  List *agg_order, Expr *agg_filter,
+				  bool agg_star, bool agg_distinct, bool func_variadic,
 				  WindowDef *over, bool is_column, int location)
 {
 	Oid			rettype;
@@ -174,8 +174,8 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 	 * the "function call" could be a projection.  We also check that there
 	 * wasn't any aggregate or variadic decoration, nor an argument name.
 	 */
-	if (nargs == 1 && agg_order == NIL && !agg_star && !agg_distinct &&
-		over == NULL && !func_variadic && argnames == NIL &&
+	if (nargs == 1 && agg_order == NIL && agg_filter == NULL && !agg_star &&
+		!agg_distinct && over == NULL && !func_variadic && argnames == NIL &&
 		list_length(funcname) == 1)
 	{
 		Oid			argtype = actual_arg_types[0];
@@ -251,6 +251,12 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 			errmsg("ORDER BY specified, but %s is not an aggregate function",
 				   NameListToString(funcname)),
 					 parser_errposition(pstate, location)));
+		if (agg_filter)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+			  errmsg("FILTER specified, but %s is not an aggregate function",
+					 NameListToString(funcname)),
+					 parser_errposition(pstate, location)));
 		if (over)
 			ereport(ERROR,
 					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
@@ -402,6 +408,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 		/* aggcollid and inputcollid will be set by parse_collate.c */
 		/* args, aggorder, aggdistinct will be set by transformAggregateCall */
 		aggref->aggstar = agg_star;
+		aggref->aggfilter = agg_filter;
 		/* agglevelsup will be set by transformAggregateCall */
 		aggref->location = location;
 
@@ -460,6 +467,7 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 		/* winref will be set by transformWindowFuncCall */
 		wfunc->winstar = agg_star;
 		wfunc->winagg = (fdresult == FUNCDETAIL_AGGREGATE);
+		wfunc->aggfilter = agg_filter;
 		wfunc->location = location;
 
 		/*
@@ -482,6 +490,16 @@ ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
 							NameListToString(funcname)),
 					 parser_errposition(pstate, location)));
 
+		/*
+		 * Reject window functions which are not aggregates in the case of
+		 * FILTER.
+		 */
+		if (!wfunc->winagg && agg_filter)
+			ereport(ERROR,
+					(errcode(ERRCODE_WRONG_OBJECT_TYPE),
+					 errmsg("FILTER is not implemented in non-aggregate window functions"),
+					 parser_errposition(pstate, location)));
+
 		/*
 		 * ordered aggs not allowed in windows yet
 		 */

src/backend/utils/adt/ruleutils.c

@@ -7424,6 +7424,13 @@ get_agg_expr(Aggref *aggref, deparse_context *context)
 		appendStringInfoString(buf, " ORDER BY ");
 		get_rule_orderby(aggref->aggorder, aggref->args, false, context);
 	}
+
+	if (aggref->aggfilter != NULL)
+	{
+		appendStringInfoString(buf, ") FILTER (WHERE ");
+		get_rule_expr((Node *) aggref->aggfilter, context, false);
+	}
+
 	appendStringInfoChar(buf, ')');
 }
 
@@ -7461,6 +7468,13 @@ get_windowfunc_expr(WindowFunc *wfunc, deparse_context *context)
 		appendStringInfoChar(buf, '*');
 	else
 		get_rule_expr((Node *) wfunc->args, context, true);
+
+	if (wfunc->aggfilter != NULL)
+	{
+		appendStringInfoString(buf, ") FILTER (WHERE ");
+		get_rule_expr((Node *) wfunc->aggfilter, context, false);
+	}
+
 	appendStringInfoString(buf, ") OVER ");
 
 	foreach(l, context->windowClause)

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201307051
+#define CATALOG_VERSION_NO	201307161
 
 #endif

src/include/nodes/execnodes.h

@@ -584,6 +584,7 @@ typedef struct AggrefExprState
 {
 	ExprState	xprstate;
 	List	   *args;			/* states of argument expressions */
+	ExprState  *aggfilter;		/* FILTER expression */
 	int			aggno;			/* ID number for agg within its plan node */
 } AggrefExprState;
 
@@ -595,6 +596,7 @@ typedef struct WindowFuncExprState
 {
 	ExprState	xprstate;
 	List	   *args;			/* states of argument expressions */
+	ExprState  *aggfilter;		/* FILTER expression */
 	int			wfuncno;		/* ID number for wfunc within its plan node */
 } WindowFuncExprState;
 

src/include/nodes/parsenodes.h

@@ -283,8 +283,8 @@ typedef struct CollateClause
  * agg_star indicates we saw a 'foo(*)' construct, while agg_distinct
  * indicates we saw 'foo(DISTINCT ...)'.  In any of these cases, the
  * construct *must* be an aggregate call.  Otherwise, it might be either an
- * aggregate or some other kind of function.  However, if OVER is present
- * it had better be an aggregate or window function.
+ * aggregate or some other kind of function.  However, if FILTER or OVER is
+ * present it had better be an aggregate or window function.
  *
  * Normally, you'd initialize this via makeFuncCall() and then only
  * change the parts of the struct its defaults don't match afterwards
@@ -297,6 +297,7 @@ typedef struct FuncCall
 	List	   *funcname;		/* qualified name of function */
 	List	   *args;			/* the arguments (list of exprs) */
 	List	   *agg_order;		/* ORDER BY (list of SortBy) */
+	Node	   *agg_filter;		/* FILTER clause, if any */
 	bool		agg_star;		/* argument was really '*' */
 	bool		agg_distinct;	/* arguments were labeled DISTINCT */
 	bool		func_variadic;	/* last argument was labeled VARIADIC */

src/include/nodes/primnodes.h

@@ -247,6 +247,7 @@ typedef struct Aggref
 	List	   *args;			/* arguments and sort expressions */
 	List	   *aggorder;		/* ORDER BY (list of SortGroupClause) */
 	List	   *aggdistinct;	/* DISTINCT (list of SortGroupClause) */
+	Expr	   *aggfilter;		/* FILTER expression */
 	bool		aggstar;		/* TRUE if argument list was really '*' */
 	Index		agglevelsup;	/* > 0 if agg belongs to outer query */
 	int			location;		/* token location, or -1 if unknown */
@@ -263,6 +264,7 @@ typedef struct WindowFunc
 	Oid			wincollid;		/* OID of collation of result */
 	Oid			inputcollid;	/* OID of collation that function should use */
 	List	   *args;			/* arguments to the window function */
+	Expr	   *aggfilter;		/* FILTER expression */
 	Index		winref;			/* index of associated WindowClause */
 	bool		winstar;		/* TRUE if argument list was really '*' */
 	bool		winagg;			/* is function a simple aggregate? */

src/include/parser/kwlist.h

@@ -155,6 +155,7 @@ PG_KEYWORD("extract", EXTRACT, COL_NAME_KEYWORD)
 PG_KEYWORD("false", FALSE_P, RESERVED_KEYWORD)
 PG_KEYWORD("family", FAMILY, UNRESERVED_KEYWORD)
 PG_KEYWORD("fetch", FETCH, RESERVED_KEYWORD)
+PG_KEYWORD("filter", FILTER, UNRESERVED_KEYWORD)
 PG_KEYWORD("first", FIRST_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("float", FLOAT_P, COL_NAME_KEYWORD)
 PG_KEYWORD("following", FOLLOWING, UNRESERVED_KEYWORD)

src/include/parser/parse_func.h

@@ -42,10 +42,9 @@ typedef enum
 } FuncDetailCode;
 
 
-extern Node *ParseFuncOrColumn(ParseState *pstate,
-				  List *funcname, List *fargs,
-				  List *agg_order, bool agg_star, bool agg_distinct,
-				  bool func_variadic,
+extern Node *ParseFuncOrColumn(ParseState *pstate, List *funcname, List *fargs,
+				  List *agg_order, Expr *agg_filter,
+				  bool agg_star, bool agg_distinct, bool func_variadic,
 				  WindowDef *over, bool is_column, int location);
 
 extern FuncDetailCode func_get_detail(List *funcname,

src/include/parser/parse_node.h

@@ -39,6 +39,7 @@ typedef enum ParseExprKind
 	EXPR_KIND_FROM_FUNCTION,	/* function in FROM clause */
 	EXPR_KIND_WHERE,			/* WHERE */
 	EXPR_KIND_HAVING,			/* HAVING */
+	EXPR_KIND_FILTER,			/* FILTER */
 	EXPR_KIND_WINDOW_PARTITION, /* window definition PARTITION BY */
 	EXPR_KIND_WINDOW_ORDER,		/* window definition ORDER BY */
 	EXPR_KIND_WINDOW_FRAME_RANGE,		/* window frame clause with RANGE */

src/test/regress/expected/aggregates.out

@@ -1154,3 +1154,98 @@ select string_agg(v, decode('ee', 'hex')) from bytea_test_table;
 (1 row)
 
 drop table bytea_test_table;
+-- FILTER tests
+select min(unique1) filter (where unique1 > 100) from tenk1;
+ min 
+-----
+ 101
+(1 row)
+
+select ten, sum(distinct four) filter (where four::text ~ '123') from onek a
+group by ten;
+ ten | sum 
+-----+-----
+   0 |    
+   1 |    
+   2 |    
+   3 |    
+   4 |    
+   5 |    
+   6 |    
+   7 |    
+   8 |    
+   9 |    
+(10 rows)
+
+select ten, sum(distinct four) filter (where four > 10) from onek a
+group by ten
+having exists (select 1 from onek b where sum(distinct a.four) = b.four);
+ ten | sum 
+-----+-----
+   0 |    
+   2 |    
+   4 |    
+   6 |    
+   8 |    
+(5 rows)
+
+select max(foo COLLATE "C") filter (where (bar collate "POSIX") > '0')
+from (values ('a', 'b')) AS v(foo,bar);
+ max 
+-----
+ a
+(1 row)
+
+-- outer reference in FILTER (PostgreSQL extension)
+select (select count(*)
+        from (values (1)) t0(inner_c))
+from (values (2),(3)) t1(outer_c); -- inner query is aggregation query
+ count 
+-------
+     1
+     1
+(2 rows)
+
+select (select count(*) filter (where outer_c <> 0)
+        from (values (1)) t0(inner_c))
+from (values (2),(3)) t1(outer_c); -- outer query is aggregation query
+ count 
+-------
+     2
+(1 row)
+
+select (select count(inner_c) filter (where outer_c <> 0)
+        from (values (1)) t0(inner_c))
+from (values (2),(3)) t1(outer_c); -- inner query is aggregation query
+ count 
+-------
+     1
+     1
+(2 rows)
+
+select
+  (select max((select i.unique2 from tenk1 i where i.unique1 = o.unique1))
+     filter (where o.unique1 < 10))
+from tenk1 o;					-- outer query is aggregation query
+ max  
+------
+ 9998
+(1 row)
+
+-- subquery in FILTER clause (PostgreSQL extension)
+select sum(unique1) FILTER (WHERE
+  unique1 IN (SELECT unique1 FROM onek where unique1 < 100)) FROM tenk1;
+ sum  
+------
+ 4950
+(1 row)
+
+-- exercise lots of aggregate parts with FILTER
+select aggfns(distinct a,b,c order by a,c using ~<~,b) filter (where a > 1)
+    from (values (1,3,'foo'),(0,null,null),(2,2,'bar'),(3,1,'baz')) v(a,b,c),
+    generate_series(1,2) i;
+          aggfns           
+---------------------------
+ {"(2,2,bar)","(3,1,baz)"}
+(1 row)
+

src/test/regress/expected/window.out

@@ -1020,5 +1020,18 @@ SELECT ntile(0) OVER (ORDER BY ten), ten, four FROM tenk1;
 ERROR:  argument of ntile must be greater than zero
 SELECT nth_value(four, 0) OVER (ORDER BY ten), ten, four FROM tenk1;
 ERROR:  argument of nth_value must be greater than zero
+-- filter
+SELECT sum(salary), row_number() OVER (ORDER BY depname), sum(
+    sum(salary) FILTER (WHERE enroll_date > '2007-01-01')
+) FILTER (WHERE depname <> 'sales') OVER (ORDER BY depname DESC) AS "filtered_sum",
+    depname
+FROM empsalary GROUP BY depname;
+  sum  | row_number | filtered_sum |  depname  
+-------+------------+--------------+-----------
+ 14600 |          3 |              | sales
+  7400 |          2 |         3500 | personnel
+ 25100 |          1 |        22600 | develop
+(3 rows)
+
 -- cleanup
 DROP TABLE empsalary;

src/test/regress/sql/aggregates.sql

@@ -442,3 +442,41 @@ select string_agg(v, NULL) from bytea_test_table;
 select string_agg(v, decode('ee', 'hex')) from bytea_test_table;
 
 drop table bytea_test_table;
+
+-- FILTER tests
+
+select min(unique1) filter (where unique1 > 100) from tenk1;
+
+select ten, sum(distinct four) filter (where four::text ~ '123') from onek a
+group by ten;
+
+select ten, sum(distinct four) filter (where four > 10) from onek a
+group by ten
+having exists (select 1 from onek b where sum(distinct a.four) = b.four);
+
+select max(foo COLLATE "C") filter (where (bar collate "POSIX") > '0')
+from (values ('a', 'b')) AS v(foo,bar);
+
+-- outer reference in FILTER (PostgreSQL extension)
+select (select count(*)
+        from (values (1)) t0(inner_c))
+from (values (2),(3)) t1(outer_c); -- inner query is aggregation query
+select (select count(*) filter (where outer_c <> 0)
+        from (values (1)) t0(inner_c))
+from (values (2),(3)) t1(outer_c); -- outer query is aggregation query
+select (select count(inner_c) filter (where outer_c <> 0)
+        from (values (1)) t0(inner_c))
+from (values (2),(3)) t1(outer_c); -- inner query is aggregation query
+select
+  (select max((select i.unique2 from tenk1 i where i.unique1 = o.unique1))
+     filter (where o.unique1 < 10))
+from tenk1 o;					-- outer query is aggregation query
+
+-- subquery in FILTER clause (PostgreSQL extension)
+select sum(unique1) FILTER (WHERE
+  unique1 IN (SELECT unique1 FROM onek where unique1 < 100)) FROM tenk1;
+
+-- exercise lots of aggregate parts with FILTER
+select aggfns(distinct a,b,c order by a,c using ~<~,b) filter (where a > 1)
+    from (values (1,3,'foo'),(0,null,null),(2,2,'bar'),(3,1,'baz')) v(a,b,c),
+    generate_series(1,2) i;

src/test/regress/sql/window.sql

@@ -264,5 +264,13 @@ SELECT ntile(0) OVER (ORDER BY ten), ten, four FROM tenk1;
 
 SELECT nth_value(four, 0) OVER (ORDER BY ten), ten, four FROM tenk1;
 
+-- filter
+
+SELECT sum(salary), row_number() OVER (ORDER BY depname), sum(
+    sum(salary) FILTER (WHERE enroll_date > '2007-01-01')
+) FILTER (WHERE depname <> 'sales') OVER (ORDER BY depname DESC) AS "filtered_sum",
+    depname
+FROM empsalary GROUP BY depname;
+
 -- cleanup
 DROP TABLE empsalary;