|
8 | 8 | * |
9 | 9 | * |
10 | 10 | * IDENTIFICATION |
11 | | - * $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.61 2003/11/2919:51:50 pgsql Exp $ |
| 11 | + * $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.62 2003/12/2921:44:49 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 | */ |
|