Index: src/backend/access/nbtree/nbtsearch.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/access/nbtree/nbtsearch.c,v
retrieving revision 1.93
diff -u -r1.93 nbtsearch.c
--- src/backend/access/nbtree/nbtsearch.c	19 Jun 2005 22:41:00 -0000	1.93
+++ src/backend/access/nbtree/nbtsearch.c	19 Sep 2005 17:37:51 -0000
@@ -647,13 +647,6 @@
 		ScanKey		cur = startKeys[i];
 
 		/*
-		 * _bt_preprocess_keys disallows it, but it's place to add some
-		 * code later
-		 */
-		if (cur->sk_flags & SK_ISNULL)
-			elog(ERROR, "btree doesn't support is(not)null, yet");
-
-		/*
 		 * If scankey operator is of default subtype, we can use the
 		 * cached comparison procedure; otherwise gotta look it up in the
 		 * catalogs.
Index: src/backend/access/nbtree/nbtutils.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/access/nbtree/nbtutils.c,v
retrieving revision 1.63
diff -u -r1.63 nbtutils.c
--- src/backend/access/nbtree/nbtutils.c	13 Jun 2005 23:14:48 -0000	1.63
+++ src/backend/access/nbtree/nbtutils.c	19 Sep 2005 17:37:52 -0000
@@ -257,12 +257,26 @@
 	if (numberOfKeys == 1)
 	{
 		/*
-		 * We don't use indices for 'A is null' and 'A is not null'
-		 * currently and 'A < = > <> NULL' will always fail - so qual is
-		 * not OK if comparison value is NULL.		- vadim 03/21/97
+		 * A IS NULL is transformed to A = NULL for index scans. 
+		 * NULL is only OK for BTEqualStrategyNumber, nothing else.
+		 * This shouldn't ever happen though, since the optimizer
+		 * should optimise away (anything op NULL). We only get here
+		 * because expand_index_quals creates it and the optimizer
+		 * doesn't touch that.
+		 *
+		 * Note the use of SK_INDEXFINDNULL. This flag needs to be
+		 * set for the index to find NULLs. This is to distinguish
+		 * the static predicate (a = NULL) which was transformed
+		 * from (a IS NULL) and the runtime predicate (a = col)
+		 * where col happend to be NULL this iteration.
 		 */
 		if (cur->sk_flags & SK_ISNULL)
-			so->qual_ok = false;
+		{
+			if( cur->sk_strategy != BTEqualStrategyNumber )
+				so->qual_ok = false;
+			else if( !(cur->sk_flags & SK_INDEXFINDNULL) )
+				so->qual_ok = false;
+		}
 		else if (relation->rd_index->indisunique &&
 				 relation->rd_rel->relnatts == 1)
 		{
@@ -306,7 +320,8 @@
 		if (i < numberOfKeys)
 		{
 			/* See comments above: any NULL implies cannot match qual */
-			if (cur->sk_flags & SK_ISNULL)
+			if (cur->sk_flags & SK_ISNULL &&
+				(cur->sk_strategy != BTEqualStrategyNumber || !(cur->sk_flags & SK_INDEXFINDNULL) ) )
 			{
 				so->qual_ok = false;
 
@@ -345,6 +360,13 @@
 
 					if (!chk || j == (BTEqualStrategyNumber - 1))
 						continue;
+					
+					/* If = NULL, cannot accept any other predicates */
+					if ( eq->sk_flags & SK_ISNULL)
+					{
+						so->qual_ok = false;
+						break;
+					}
 					test = FunctionCall2(&chk->sk_func,
 										 eq->sk_argument,
 										 chk->sk_argument);
@@ -445,6 +467,17 @@
 		/* have we seen one of these before? */
 		if (xform[j])
 		{
+			/* If matching NULL, we can *only* match null */
+			if ( (cur->sk_flags ^ xform[j]->sk_flags) & SK_ISNULL)
+			{
+				so->qual_ok = false;
+				continue;
+			}
+			/* If both = NULL, goto next attr */
+			if( cur->sk_flags & SK_ISNULL )
+			{
+				continue;
+			}
 			/* yup, keep the more restrictive key */
 			test = FunctionCall2(&cur->sk_func,
 								 cur->sk_argument,
@@ -515,12 +548,18 @@
 							  tupdesc,
 							  &isNull);
 
-		/* btree doesn't support 'A is null' clauses, yet */
 		if (key->sk_flags & SK_ISNULL)
 		{
-			/* we shouldn't get here, really; see _bt_preprocess_keys() */
-			*continuescan = false;
-			return false;
+			/* If the scankey is null, it must be
+			 * BTEqualStrategyNumber. The comment below applies
+			 * here too: if we're at a not null value on a
+			 * required key, we must be at a point where it is
+			 * no longer useful to proceed. */
+			
+			if( !isNull && ikey < so->numberOfRequiredKeys )
+				*continuescan = false;
+
+			return isNull;
 		}
 
 		if (isNull)
Index: src/backend/executor/nodeIndexscan.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/executor/nodeIndexscan.c,v
retrieving revision 1.103
diff -u -r1.103 nodeIndexscan.c
--- src/backend/executor/nodeIndexscan.c	6 May 2005 17:24:54 -0000	1.103
+++ src/backend/executor/nodeIndexscan.c	19 Sep 2005 17:37:53 -0000
@@ -624,10 +624,14 @@
 			/*
 			 * if the rightop is a const node then it means it
 			 * identifies the value to place in our scan key.
+			 *
+			 * We need SK_INDEXFINDNULL for IS NULL to work, for
+			 * runtime keys a NULL is special and shouldn't
+			 * match anything.
 			 */
 			scanvalue = ((Const *) rightop)->constvalue;
 			if (((Const *) rightop)->constisnull)
-				flags |= SK_ISNULL;
+				flags |= SK_ISNULL | SK_INDEXFINDNULL;
 		}
 		else
 		{
Index: src/backend/optimizer/path/indxpath.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/optimizer/path/indxpath.c,v
retrieving revision 1.188
diff -u -r1.188 indxpath.c
--- src/backend/optimizer/path/indxpath.c	28 Aug 2005 22:47:20 -0000	1.188
+++ src/backend/optimizer/path/indxpath.c	19 Sep 2005 17:37:53 -0000
@@ -816,6 +816,13 @@
 		if (match_boolean_index_clause((Node *) clause, indexcol, index))
 			return true;
 	}
+	
+	if( IsA( clause, NullTest ) && ((NullTest*)clause)->nulltesttype == IS_NULL )
+	{
+		leftop = (Node*) ((NullTest*)clause)->arg;
+		if (match_index_to_operand(leftop, indexcol, index))
+			return true;
+	}
 
 	/* Else clause must be a binary opclause. */
 	if (!is_opclause(clause))
@@ -1928,6 +1935,18 @@
 					continue;
 				}
 			}
+			
+			/* IS NULL case */
+			if( IsA( rinfo->clause, NullTest ) )
+			{
+				Oid	eqop = get_opclass_member(curClass, InvalidOid, BTEqualStrategyNumber);
+				Expr *arg = ((NullTest*)(rinfo->clause))->arg;
+				Expr *opclause = make_opclause(eqop, BOOLOID, false, arg, (Expr *) makeNullConst(exprType(arg)) );
+
+				resultquals = lappend(resultquals, make_restrictinfo( opclause, true, NULL ) );
+				
+				continue;
+			}
 
 			resultquals = list_concat(resultquals,
 									  expand_indexqual_condition(rinfo,
Index: src/include/access/skey.h
===================================================================
RCS file: /projects/cvsroot/pgsql/src/include/access/skey.h,v
retrieving revision 1.29
diff -u -r1.29 skey.h
--- src/include/access/skey.h	24 Jun 2005 00:18:52 -0000	1.29
+++ src/include/access/skey.h	19 Sep 2005 17:37:55 -0000
@@ -73,7 +73,7 @@
 #define SK_ISNULL		0x0001	/* sk_argument is NULL */
 #define SK_UNARY		0x0002	/* unary operator (currently unsupported) */
 #define SK_NEGATE		0x0004	/* must negate the function result */
-
+#define SK_INDEXFINDNULL	0x0008  /* index can find NULL with SK_ISNULL here */
 
 /*
  * prototypes for functions in access/common/scankey.c