Support ORDER BY ... NULLS FIRST/LAST, and add ASC/DESC/NULLS FIRST/NULLS LAST

per-column options for btree indexes.  The planner's support for this is still
pretty rudimentary; it does not yet know how to plan mergejoins with
nondefault ordering options.  The documentation is pretty rudimentary, too.
I'll work on improving that stuff later.

Note incompatible change from prior behavior: ORDER BY ... USING will now be
rejected if the operator is not a less-than or greater-than member of some
btree opclass.  This prevents less-than-sane behavior if an operator that
doesn't actually define a proper sort ordering is selected.

1 files changed, 61 insertions, 5 deletions

diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index e35d6479db6..bbaa34f758a 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/indexcmds.c,v 1.151 2007/01/05 22:19:26 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/indexcmds.c,v 1.152 2007/01/09 02:14:11 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -49,10 +49,13 @@
 
 /* non-export function prototypes */
 static void CheckPredicate(Expr *predicate);
-static void ComputeIndexAttrs(IndexInfo *indexInfo, Oid *classOidP,
+static void ComputeIndexAttrs(IndexInfo *indexInfo,
+				  Oid *classOidP,
+				  int16 *colOptionP,
 				  List *attList,
 				  Oid relId,
 				  char *accessMethodName, Oid accessMethodId,
+				  bool amcanorder,
 				  bool isconstraint);
 static Oid GetIndexOpClass(List *opclass, Oid attrType,
 				char *accessMethodName, Oid accessMethodId);
@@ -115,8 +118,10 @@ DefineIndex(RangeVar *heapRelation,
 	Relation	rel;
 	HeapTuple	tuple;
 	Form_pg_am	accessMethodForm;
+	bool		amcanorder;
 	RegProcedure amoptions;
 	Datum		reloptions;
+	int16	   *coloptions;
 	IndexInfo  *indexInfo;
 	int			numberOfAttributes;
 	List	   *old_xact_list;
@@ -290,6 +295,8 @@ DefineIndex(RangeVar *heapRelation,
 		  errmsg("access method \"%s\" does not support multicolumn indexes",
 				 accessMethodName)));
 
+	amcanorder = (accessMethodForm->amorderstrategy > 0);
+
 	amoptions = accessMethodForm->amoptions;
 
 	ReleaseSysCache(tuple);
@@ -419,9 +426,10 @@ DefineIndex(RangeVar *heapRelation,
 	indexInfo->ii_Concurrent = concurrent;
 
 	classObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
-	ComputeIndexAttrs(indexInfo, classObjectId, attributeList,
+	coloptions = (int16 *) palloc(numberOfAttributes * sizeof(int16));
+	ComputeIndexAttrs(indexInfo, classObjectId, coloptions, attributeList,
 					  relationId, accessMethodName, accessMethodId,
-					  isconstraint);
+					  amcanorder, isconstraint);
 
 	heap_close(rel, NoLock);
 
@@ -439,7 +447,7 @@ DefineIndex(RangeVar *heapRelation,
 	indexRelationId =
 		index_create(relationId, indexRelationName, indexRelationId,
 					 indexInfo, accessMethodId, tablespaceId, classObjectId,
-					 reloptions, primary, isconstraint,
+					 coloptions, reloptions, primary, isconstraint,
 					 allowSystemTableMods, skip_build, concurrent);
 
 	if (!concurrent)
@@ -585,13 +593,19 @@ CheckPredicate(Expr *predicate)
 		   errmsg("functions in index predicate must be marked IMMUTABLE")));
 }
 
+/*
+ * Compute per-index-column information, including indexed column numbers
+ * or index expressions, opclasses, and indoptions.
+ */
 static void
 ComputeIndexAttrs(IndexInfo *indexInfo,
 				  Oid *classOidP,
+				  int16 *colOptionP,
 				  List *attList,	/* list of IndexElem's */
 				  Oid relId,
 				  char *accessMethodName,
 				  Oid accessMethodId,
+				  bool amcanorder,
 				  bool isconstraint)
 {
 	ListCell   *rest;
@@ -605,6 +619,9 @@ ComputeIndexAttrs(IndexInfo *indexInfo,
 		IndexElem  *attribute = (IndexElem *) lfirst(rest);
 		Oid			atttype;
 
+		/*
+		 * Process the column-or-expression to be indexed.
+		 */
 		if (attribute->name != NULL)
 		{
 			/* Simple index attribute */
@@ -674,10 +691,49 @@ ComputeIndexAttrs(IndexInfo *indexInfo,
 						 errmsg("functions in index expression must be marked IMMUTABLE")));
 		}
 
+		/*
+		 * Identify the opclass to use.
+		 */
 		classOidP[attn] = GetIndexOpClass(attribute->opclass,
 										  atttype,
 										  accessMethodName,
 										  accessMethodId);
+
+		/*
+		 * Set up the per-column options (indoption field).  For now, this
+		 * is zero for any un-ordered index, while ordered indexes have DESC
+		 * and NULLS FIRST/LAST options.
+		 */
+		colOptionP[attn] = 0;
+		if (amcanorder)
+		{
+			/* default ordering is ASC */
+			if (attribute->ordering == SORTBY_DESC)
+				colOptionP[attn] |= INDOPTION_DESC;
+			/* default null ordering is LAST for ASC, FIRST for DESC */
+			if (attribute->nulls_ordering == SORTBY_NULLS_DEFAULT)
+			{
+				if (attribute->ordering == SORTBY_DESC)
+					colOptionP[attn] |= INDOPTION_NULLS_FIRST;
+			}
+			else if (attribute->nulls_ordering == SORTBY_NULLS_FIRST)
+				colOptionP[attn] |= INDOPTION_NULLS_FIRST;
+		}
+		else
+		{
+			/* index AM does not support ordering */
+			if (attribute->ordering != SORTBY_DEFAULT)
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("access method \"%s\" does not support ASC/DESC options",
+								accessMethodName)));
+			if (attribute->nulls_ordering != SORTBY_NULLS_DEFAULT)
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("access method \"%s\" does not support NULLS FIRST/LAST options",
+								accessMethodName)));
+		}
+
 		attn++;
 	}
 }