Redesign DISTINCT ON as discussed in pgsql-sql 1/25/00: syntax is now

SELECT DISTINCT ON (expr [, expr ...]) targetlist ...
and there is a check to make sure that the user didn't specify an ORDER BY
that's incompatible with the DISTINCT operation.
Reimplement nodeUnique and nodeGroup to use the proper datatype-specific
equality function for each column being compared --- they used to do
bitwise comparisons or convert the data to text strings and strcmp().
(To add insult to injury, they'd look up the conversion functions once
for each tuple...)  Parse/plan representation of DISTINCT is now a list
of SortClause nodes.
initdb forced by querytree change...

1 files changed, 22 insertions, 10 deletions

diff --git a/src/backend/optimizer/prep/prepunion.c b/src/backend/optimizer/prep/prepunion.c
index a27305ef3e8..4323b652e8d 100644
--- a/src/backend/optimizer/prep/prepunion.c
+++ b/src/backend/optimizer/prep/prepunion.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.41 2000/01/26 05:56:39 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.42 2000/01/27 18:11:32 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -21,6 +21,7 @@
 #include "optimizer/planmain.h"
 #include "optimizer/planner.h"
 #include "optimizer/prep.h"
+#include "optimizer/tlist.h"
 #include "parser/parse_clause.h"
 #include "parser/parsetree.h"
 #include "utils/lsyscache.h"
@@ -131,7 +132,7 @@ plan_union_queries(Query *parse)
 			!last_union_all_flag)
 		{
 			parse->sortClause = NIL;
-			parse->uniqueFlag = NULL;
+			parse->distinctClause = NIL;
 		}
 
 		parse->unionClause = NIL;		/* prevent recursion */
@@ -183,17 +184,28 @@ plan_union_queries(Query *parse)
 	if (!last_union_all_flag)
 	{
 		/* Need SELECT DISTINCT behavior to implement UNION.
-		 * Set uniqueFlag properly, put back the held sortClause,
-		 * and add any missing columns to the sort clause.
+		 * Put back the held sortClause, add any missing columns to the
+		 * sort clause, and set distinctClause properly.
 		 */
-		parse->uniqueFlag = "*";
+		List	   *slitem;
+
 		parse->sortClause = addAllTargetsToSortList(hold_sortClause,
 													parse->targetList);
+		parse->distinctClause = NIL;
+		foreach(slitem, parse->sortClause)
+		{
+			SortClause *scl = (SortClause *) lfirst(slitem);
+			TargetEntry *tle = get_sortgroupclause_tle(scl, parse->targetList);
+
+			if (! tle->resdom->resjunk)
+				parse->distinctClause = lappend(parse->distinctClause,
+												copyObject(scl));
+		}
 	}
 	else
 	{
-		/* needed so we don't take the flag from the first query */
-		parse->uniqueFlag = NULL;
+		/* needed so we don't take SELECT DISTINCT from the first query */
+		parse->distinctClause = NIL;
 	}
 
 	/* Make sure we don't try to apply the first query's grouping stuff
@@ -314,9 +326,9 @@ plan_inherit_query(Relids relids,
 		 * Clear the sorting and grouping qualifications in the subquery,
 		 * so that sorting will only be done once after append
 		 */
-		new_root->uniqueFlag = NULL;
-		new_root->sortClause = NULL;
-		new_root->groupClause = NULL;
+		new_root->distinctClause = NIL;
+		new_root->sortClause = NIL;
+		new_root->groupClause = NIL;
 		new_root->havingQual = NULL;
 		new_root->hasAggs = false; /* shouldn't be any left ... */