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

4 files changed, 14 insertions, 3 deletions

diff --git a/src/include/parser/kwlist.h b/src/include/parser/kwlist.h
index 8bd34d6e8f..ab2715629c 100644
--- a/src/include/parser/kwlist.h
+++ b/src/include/parser/kwlist.h
@@ -412,6 +412,7 @@ PG_KEYWORD("where", WHERE, RESERVED_KEYWORD)
 PG_KEYWORD("whitespace", WHITESPACE_P, UNRESERVED_KEYWORD)
 PG_KEYWORD("window", WINDOW, RESERVED_KEYWORD)
 PG_KEYWORD("with", WITH, RESERVED_KEYWORD)
+PG_KEYWORD("within", WITHIN, UNRESERVED_KEYWORD)
 PG_KEYWORD("without", WITHOUT, UNRESERVED_KEYWORD)
 PG_KEYWORD("work", WORK, UNRESERVED_KEYWORD)
 PG_KEYWORD("wrapper", WRAPPER, UNRESERVED_KEYWORD)
diff --git a/src/include/parser/parse_agg.h b/src/include/parser/parse_agg.h
index b6d9dd37b0..487d5cc889 100644
--- a/src/include/parser/parse_agg.h
+++ b/src/include/parser/parse_agg.h
@@ -23,8 +23,17 @@ extern void transformWindowFuncCall(ParseState *pstate, WindowFunc *wfunc,
 
 extern void parseCheckAggregates(ParseState *pstate, Query *qry);
 
+extern int	get_aggregate_argtypes(Aggref *aggref, Oid *inputTypes);
+
+extern Oid resolve_aggregate_transtype(Oid aggfuncid,
+							Oid aggtranstype,
+							Oid *inputTypes,
+							int numArguments);
+
 extern void build_aggregate_fnexprs(Oid *agg_input_types,
 						int agg_num_inputs,
+						int agg_num_direct_inputs,
+						bool agg_ordered_set,
 						bool agg_variadic,
 						Oid agg_state_type,
 						Oid agg_result_type,
diff --git a/src/include/parser/parse_clause.h b/src/include/parser/parse_clause.h
index 9bdb03347a..18f338d340 100644
--- a/src/include/parser/parse_clause.h
+++ b/src/include/parser/parse_clause.h
@@ -42,6 +42,9 @@ extern List *transformDistinctClause(ParseState *pstate,
 extern List *transformDistinctOnClause(ParseState *pstate, List *distinctlist,
 						  List **targetlist, List *sortClause);
 
+extern List *addTargetToSortList(ParseState *pstate, TargetEntry *tle,
+					List *sortlist, List *targetlist, SortBy *sortby,
+					bool resolveUnknown);
 extern Index assignSortGroupRef(TargetEntry *tle, List *tlist);
 extern bool targetIsInSortList(TargetEntry *tle, Oid sortop, List *sortList);
 
diff --git a/src/include/parser/parse_func.h b/src/include/parser/parse_func.h
index d33eef3482..f28fd9974c 100644
--- a/src/include/parser/parse_func.h
+++ b/src/include/parser/parse_func.h
@@ -43,9 +43,7 @@ typedef enum
 
 
 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);
+				  FuncCall *fn, int location);
 
 extern FuncDetailCode func_get_detail(List *funcname,
 				List *fargs, List *fargnames,