Support ordered-set (WITHIN GROUP) aggregates.

This patch introduces generic support for ordered-set and hypothetical-set
aggregate functions, as well as implementations of the instances defined in
SQL:2008 (percentile_cont(), percentile_disc(), rank(), dense_rank(),
percent_rank(), cume_dist()).  We also added mode() though it is not in the
spec, as well as versions of percentile_cont() and percentile_disc() that
can compute multiple percentile values in one pass over the data.

Unlike the original submission, this patch puts full control of the sorting
process in the hands of the aggregate's support functions.  To allow the
support functions to find out how they're supposed to sort, a new API
function AggGetAggref() is added to nodeAgg.c.  This allows retrieval of
the aggregate call's Aggref node, which may have other uses beyond the
immediate need.  There is also support for ordered-set aggregates to
install cleanup callback functions, so that they can be sure that
infrastructure such as tuplesort objects gets cleaned up.

In passing, make some fixes in the recently-added support for variadic
aggregates, and make some editorial adjustments in the recent FILTER
additions for aggregates.  Also, simplify use of IsBinaryCoercible() by
allowing it to succeed whenever the target type is ANY or ANYELEMENT.
It was inconsistent that it dealt with other polymorphic target types
but not these.

Atri Sharma and Andrew Gierth; reviewed by Pavel Stehule and Vik Fearing,
and rather heavily editorialized upon by Tom Lane

1 files changed, 8 insertions, 0 deletions

diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
index d7db67dc9ea..17626f9bdce 100644
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -1453,6 +1453,10 @@ exprLocation(const Node *expr)
 		case T_Constraint:
 			loc = ((const Constraint *) expr)->location;
 			break;
+		case T_FunctionParameter:
+			/* just use typename's location */
+			loc = exprLocation((Node *) ((const FunctionParameter *) expr)->argType);
+			break;
 		case T_XmlSerialize:
 			/* XMLSERIALIZE keyword should always be the first thing */
 			loc = ((const XmlSerialize *) expr)->location;
@@ -1625,6 +1629,9 @@ expression_tree_walker(Node *node,
 				Aggref	   *expr = (Aggref *) node;
 
 				/* recurse directly on List */
+				if (expression_tree_walker((Node *) expr->aggdirectargs,
+										   walker, context))
+					return true;
 				if (expression_tree_walker((Node *) expr->args,
 										   walker, context))
 					return true;
@@ -2157,6 +2164,7 @@ expression_tree_mutator(Node *node,
 				Aggref	   *newnode;
 
 				FLATCOPY(newnode, aggref, Aggref);
+				MUTATE(newnode->aggdirectargs, aggref->aggdirectargs, List *);
 				MUTATE(newnode->args, aggref->args, List *);
 				MUTATE(newnode->aggorder, aggref->aggorder, List *);
 				MUTATE(newnode->aggdistinct, aggref->aggdistinct, List *);