Make 'col IS NULL' clauses be indexable conditions.

Teodor Sigaev, with some kibitzing from Tom Lane.

src/backend/optimizer/path/indxpath.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.218 2007/03/21 22:18:12 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.219 2007/04/06 22:33:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1050,6 +1050,7 @@ match_clause_to_indexcol(IndexOptInfo *index,
 	 * Clause must be a binary opclause, or possibly a ScalarArrayOpExpr
 	 * (which is always binary, by definition).  Or it could be a
 	 * RowCompareExpr, which we pass off to match_rowcompare_to_indexcol().
+	 * Or, if the index supports it, we can handle IS NULL clauses.
 	 */
 	if (is_opclause(clause))
 	{
@@ -1083,6 +1084,15 @@ match_clause_to_indexcol(IndexOptInfo *index,
 											(RowCompareExpr *) clause,
 											outer_relids);
 	}
+	else if (index->amsearchnulls && IsA(clause, NullTest))
+	{
+		NullTest	*nt = (NullTest *) clause;
+
+		if (nt->nulltesttype == IS_NULL &&
+			match_index_to_operand((Node *) nt->arg, indexcol, index))
+			return true;
+		return false;
+	}
 	else
 		return false;
 
@@ -2102,8 +2112,8 @@ expand_indexqual_conditions(IndexOptInfo *index, List *clausegroups)
 			}
 
 			/*
-			 * Else it must be an opclause (usual case), ScalarArrayOp, or
-			 * RowCompare
+			 * Else it must be an opclause (usual case), ScalarArrayOp,
+			 * RowCompare, or NullTest
 			 */
 			if (is_opclause(clause))
 			{
@@ -2123,6 +2133,16 @@ expand_indexqual_conditions(IndexOptInfo *index, List *clausegroups)
 																  index,
 																  indexcol));
 			}
+			else if (IsA(clause, NullTest))
+			{
+				Assert(index->amsearchnulls);
+				resultquals = lappend(resultquals,
+									  make_restrictinfo(clause,
+														true,
+														false,
+														false,
+														NULL));
+			}
 			else
 				elog(ERROR, "unsupported indexqual type: %d",
 					 (int) nodeTag(clause));

src/backend/optimizer/plan/createplan.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.227 2007/02/25 17:44:01 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/createplan.c,v 1.228 2007/04/06 22:33:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -18,6 +18,7 @@
 
 #include <limits.h>
 
+#include "access/skey.h"
 #include "nodes/makefuncs.h"
 #include "optimizer/clauses.h"
 #include "optimizer/cost.h"
@@ -1821,6 +1822,7 @@ fix_indexqual_references(List *indexquals, IndexPath *index_path,
 		Oid			stratlefttype;
 		Oid			stratrighttype;
 		bool		recheck;
+		bool		is_null_op = false;
 
 		Assert(IsA(rinfo, RestrictInfo));
 
@@ -1907,6 +1909,17 @@ fix_indexqual_references(List *indexquals, IndexPath *index_path,
 														 &opfamily);
 			clause_op = saop->opno;
 		}
+		else if (IsA(clause, NullTest))
+		{
+			NullTest *nt = (NullTest *) clause;
+
+			Assert(nt->nulltesttype == IS_NULL);
+			nt->arg = (Expr *) fix_indexqual_operand((Node *) nt->arg,
+													 index,
+													 &opfamily);
+			is_null_op = true;
+			clause_op = InvalidOid;		/* keep compiler quiet */
+		}
 		else
 		{
 			elog(ERROR, "unsupported indexqual type: %d",
@@ -1916,16 +1929,27 @@ fix_indexqual_references(List *indexquals, IndexPath *index_path,
 
 		*fixed_indexquals = lappend(*fixed_indexquals, clause);
 
-		/*
-		 * Look up the (possibly commuted) operator in the operator family to
-		 * get its strategy number and the recheck indicator.	This also
-		 * double-checks that we found an operator matching the index.
-		 */
-		get_op_opfamily_properties(clause_op, opfamily,
-								   &stratno,
-								   &stratlefttype,
-								   &stratrighttype,
-								   &recheck);
+		if (is_null_op)
+		{
+			/* IS NULL doesn't have a clause_op */
+			stratno = InvalidStrategy;
+			stratrighttype = InvalidOid;
+			/* We assume it's non-lossy ... might need more work someday */
+			recheck = false;
+		}
+		else
+		{
+			/*
+			 * Look up the (possibly commuted) operator in the operator family
+			 * to get its strategy number and the recheck indicator. This also
+			 * double-checks that we found an operator matching the index.
+			 */
+			get_op_opfamily_properties(clause_op, opfamily,
+									   &stratno,
+									   &stratlefttype,
+									   &stratrighttype,
+									   &recheck);
+		}
 
 		*indexstrategy = lappend_int(*indexstrategy, stratno);
 		*indexsubtype = lappend_oid(*indexsubtype, stratrighttype);

src/backend/optimizer/util/plancat.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.132 2007/01/20 23:13:01 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/plancat.c,v 1.133 2007/04/06 22:33:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -187,6 +187,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 			info->relam = indexRelation->rd_rel->relam;
 			info->amcostestimate = indexRelation->rd_am->amcostestimate;
 			info->amoptionalkey = indexRelation->rd_am->amoptionalkey;
+			info->amsearchnulls = indexRelation->rd_am->amsearchnulls;
 
 			/*
 			 * Fetch the ordering operators associated with the index, if any.