Improve comment.

tglsfdc · tglsfdc · commit b53ca9bbcb28 · 2003-12-29T21:44:49.000Z
diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.61 2003/11/29 19:51:50 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.62 2003/12/29 21:44:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -108,6 +108,10 @@ restrictlist_selectivity(Query *root,
  * If the calculation yields zero or negative, however, we chicken out and
  * use a default estimate; that probably means that one or both
  * selectivities is a default estimate rather than an actual range value.
+ *
+ * A free side-effect is that we can recognize redundant inequalities such
+ * as "x < 4 AND x < 5"; only the tighter constraint will be counted.
+ *
  * Of course this is all very dependent on the behavior of
  * scalarltsel/scalargtsel; perhaps some day we can generalize the approach.
  */

Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@`
`8`	`8`	`*`
`9`	`9`	`*`
`10`	`10`	`* IDENTIFICATION`
`11`		`- * $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.61 2003/11/29 19:51:50 pgsql Exp $`
	`11`	`+ * $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.62 2003/12/29 21:44:49 tgl Exp $`
`12`	`12`	`*`
`13`	`13`	`*-------------------------------------------------------------------------`
`14`	`14`	`*/`
`@@ -108,6 +108,10 @@ restrictlist_selectivity(Query *root,`
`108`	`108`	`* If the calculation yields zero or negative, however, we chicken out and`
`109`	`109`	`* use a default estimate; that probably means that one or both`
`110`	`110`	`* selectivities is a default estimate rather than an actual range value.`
	`111`	`+ *`
	`112`	`+ * A free side-effect is that we can recognize redundant inequalities such`
	`113`	`+ * as "x < 4 AND x < 5"; only the tighter constraint will be counted.`
	`114`	`+ *`
`111`	`115`	`* Of course this is all very dependent on the behavior of`
`112`	`116`	`* scalarltsel/scalargtsel; perhaps some day we can generalize the approach.`
`113`	`117`	`*/`