Rearrange the querytree representation of ORDER BY/GROUP BY/DISTINCT items

as per my recent proposal:

1. Fold SortClause and GroupClause into a single node type SortGroupClause.
We were already relying on them to be struct-equivalent, so using two node
tags wasn't accomplishing much except to get in the way of comparing items
with equal().

2. Add an "eqop" field to SortGroupClause to carry the associated equality
operator.  This is cheap for the parser to get at the same time it's looking
up the sort operator, and storing it eliminates the need for repeated
not-so-cheap lookups during planning.  In future this will also let us
represent GROUP/DISTINCT operations on datatypes that have hash opclasses
but no btree opclasses (ie, they have equality but no natural sort order).
The previous representation simply didn't work for that, since its only
indicator of comparison semantics was a sort operator.

3. Add a hasDistinctOn boolean to struct Query to explicitly record whether
the distinctClause came from DISTINCT or DISTINCT ON.  This allows removing
some complicated and not 100% bulletproof code that attempted to figure
that out from the distinctClause alone.

This patch doesn't in itself create any new capability, but it's necessary
infrastructure for future attempts to use hash-based grouping for DISTINCT
and UNION/INTERSECT/EXCEPT.

2 files changed, 12 insertions, 14 deletions

diff --git a/src/include/parser/parse_clause.h b/src/include/parser/parse_clause.h
index 6fc357522e7..357a2947cb5 100644
--- a/src/include/parser/parse_clause.h
+++ b/src/include/parser/parse_clause.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/parser/parse_clause.h,v 1.50 2008/07/31 22:47:56 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/parser/parse_clause.h,v 1.51 2008/08/02 21:32:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -30,13 +30,14 @@ extern List *transformGroupClause(ParseState *pstate, List *grouplist,
 					 List **targetlist, List *sortClause);
 extern List *transformSortClause(ParseState *pstate, List *orderlist,
 					List **targetlist, bool resolveUnknown);
-extern List *transformDistinctClause(ParseState *pstate, List *distinctlist,
+extern List *transformDistinctClause(ParseState *pstate,
+						List **targetlist, List *sortClause);
+extern List *transformDistinctOnClause(ParseState *pstate, List *distinctlist,
 						List **targetlist, List *sortClause);
 
-extern List *addTargetToSortList(ParseState *pstate, TargetEntry *tle,
-					List *sortlist, List *targetlist,
-					SortByDir sortby_dir, SortByNulls sortby_nulls,
-					List *sortby_opname, bool resolveUnknown);
+extern List *addTargetToGroupList(ParseState *pstate, TargetEntry *tle,
+					 List *grouplist, List *targetlist,
+					 bool requireSortOp, 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_oper.h b/src/include/parser/parse_oper.h
index f0ec2d1f088..ad0d65b3be2 100644
--- a/src/include/parser/parse_oper.h
+++ b/src/include/parser/parse_oper.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/parser/parse_oper.h,v 1.42 2008/01/01 19:45:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/parser/parse_oper.h,v 1.43 2008/08/02 21:32:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -45,16 +45,13 @@ extern Operator compatible_oper(ParseState *pstate, List *op,
 
 /* currently no need for compatible_left_oper/compatible_right_oper */
 
-/* Routines for identifying "=", "<", ">" operators for a type */
-extern Operator equality_oper(Oid argtype, bool noError);
-extern Operator ordering_oper(Oid argtype, bool noError);
-extern Operator reverse_ordering_oper(Oid argtype, bool noError);
+/* Routines for identifying "<", "=", ">" operators for a type */
+extern void get_sort_group_operators(Oid argtype,
+						 bool needLT, bool needEQ, bool needGT,
+						 Oid *ltOpr, Oid *eqOpr, Oid *gtOpr);
 
 /* Convenience routines for common calls on the above */
 extern Oid	compatible_oper_opid(List *op, Oid arg1, Oid arg2, bool noError);
-extern Oid	equality_oper_funcid(Oid argtype);
-extern Oid	ordering_oper_opid(Oid argtype);
-extern Oid	reverse_ordering_oper_opid(Oid argtype);
 
 /* Extract operator OID or underlying-function OID from an Operator tuple */
 extern Oid	oprid(Operator op);