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, 5 insertions, 8 deletions

diff --git a/src/include/optimizer/clauses.h b/src/include/optimizer/clauses.h
index dce10d65066..69a4f4c774c 100644
--- a/src/include/optimizer/clauses.h
+++ b/src/include/optimizer/clauses.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/optimizer/clauses.h,v 1.90 2008/04/01 00:48:33 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/clauses.h,v 1.91 2008/08/02 21:32:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -63,9 +63,6 @@ extern Relids find_nonnullable_rels(Node *clause);
 extern bool is_pseudo_constant_clause(Node *clause);
 extern bool is_pseudo_constant_clause_relids(Node *clause, Relids relids);
 
-extern bool has_distinct_clause(Query *query);
-extern bool has_distinct_on_clause(Query *query);
-
 extern int	NumRelids(Node *clause);
 
 extern void CommuteOpExpr(OpExpr *clause);
diff --git a/src/include/optimizer/tlist.h b/src/include/optimizer/tlist.h
index e953d665209..8a8966213b1 100644
--- a/src/include/optimizer/tlist.h
+++ b/src/include/optimizer/tlist.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/optimizer/tlist.h,v 1.49 2008/01/01 19:45:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/tlist.h,v 1.50 2008/08/02 21:32:01 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -25,11 +25,11 @@ extern List *add_to_flat_tlist(List *tlist, List *vars);
 
 extern TargetEntry *get_sortgroupref_tle(Index sortref,
 					 List *targetList);
-extern TargetEntry *get_sortgroupclause_tle(SortClause *sortClause,
+extern TargetEntry *get_sortgroupclause_tle(SortGroupClause *sgClause,
 						List *targetList);
-extern Node *get_sortgroupclause_expr(SortClause *sortClause,
+extern Node *get_sortgroupclause_expr(SortGroupClause *sgClause,
 						 List *targetList);
-extern List *get_sortgrouplist_exprs(List *sortClauses,
+extern List *get_sortgrouplist_exprs(List *sgClauses,
 						List *targetList);
 
 extern bool tlist_same_datatypes(List *tlist, List *colTypes, bool junkOK);