index edde32d12dfd9b82eefe54cc7b40173fd9080952..967536393eec0621f37430cb886635b45b07555c 100644 (file)
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.140 2005年03月27日 23:53:02 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/path/costsize.c,v 1.141 2005年04月04日 01:43:12 tgl Exp $
*
*-------------------------------------------------------------------------
*/
rescanratio = 1.0 + (rescannedtuples / inner_path_rows);
/*
- * A merge join will stop as soon as it exhausts either input stream.
- * Estimate fraction of the left and right inputs that will actually
- * need to be scanned. We use only the first (most significant) merge
- * clause for this purpose.
+ * A merge join will stop as soon as it exhausts either input stream
+ * (unless it's an outer join, in which case the outer side has to be
+ * scanned all the way anyway). Estimate fraction of the left and right
+ * inputs that will actually need to be scanned. We use only the first
+ * (most significant) merge clause for this purpose.
*
* Since this calculation is somewhat expensive, and will be the same for
* all mergejoin paths associated with the merge clause, we cache the
* results in the RestrictInfo node.
*/
- if (mergeclauses)
+ if (mergeclauses && path->jpath.jointype != JOIN_FULL)
{
firstclause = (RestrictInfo *) linitial(mergeclauses);
if (firstclause->left_mergescansel < 0) /* not computed yet? */
outerscansel = firstclause->right_mergescansel;
innerscansel = firstclause->left_mergescansel;
}
+ if (path->jpath.jointype == JOIN_LEFT)
+ outerscansel = 1.0;
+ else if (path->jpath.jointype == JOIN_RIGHT)
+ innerscansel = 1.0;
}
else
{
- /* cope with clauseless mergejoin */
+ /* cope with clauseless or full mergejoin */
outerscansel = innerscansel = 1.0;
}