Support "x IS NOT NULL" clauses as indexscan conditions. This turns out

to be just a minor extension of the previous patch that made "x IS NULL"
indexable, because we can treat the IS NOT NULL condition as if it were
"x < NULL" or "x > NULL" (depending on the index's NULLS FIRST/LAST option),
just like IS NULL is treated like "x = NULL".  Aside from any possible
usefulness in its own right, this is an important improvement for
index-optimized MAX/MIN aggregates: it is now reliably possible to get
a column's min or max value cheaply, even when there are a lot of nulls
cluttering the interesting end of the index.

1 files changed, 3 insertions, 4 deletions

diff --git a/src/backend/optimizer/path/indxpath.c b/src/backend/optimizer/path/indxpath.c
index 7bb5d8993cc..456a5b9be48 100644
--- a/src/backend/optimizer/path/indxpath.c
+++ b/src/backend/optimizer/path/indxpath.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.242 2009/09/17 20:49:28 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.243 2010/01/01 21:53:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1218,7 +1218,7 @@ 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.
+	 * Or, if the index supports it, we can handle IS NULL/NOT NULL clauses.
 	 */
 	if (is_opclause(clause))
 	{
@@ -1256,8 +1256,7 @@ match_clause_to_indexcol(IndexOptInfo *index,
 	{
 		NullTest   *nt = (NullTest *) clause;
 
-		if (nt->nulltesttype == IS_NULL &&
-			match_index_to_operand((Node *) nt->arg, indexcol, index))
+		if (match_index_to_operand((Node *) nt->arg, indexcol, index))
 			return true;
 		return false;
 	}