index 4858f985cffe2eb0f1f061a866aba3d7a996c37a..52dd8c22ca7457002808cbcd2324f8cbc5d7532e 100644 (file)
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.229 2007年01月10日 18:06:04 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.230 2007年01月17日 17:25:52 tgl Exp $
*
* HISTORY
* AUTHOR DATE MAJOR EVENT
@@ -1073,6 +1073,12 @@ is_strict_saop(ScalarArrayOpExpr *expr, bool falseOK)
* may vary from one statement to the next. However, the expr's value
* will be constant over any one scan of the current query, so it can be
* used as, eg, an indexscan key.
+ *
+ * CAUTION: this function omits to test for one very important class of
+ * not-constant expressions, namely aggregates (Aggrefs). In current usage
+ * this is only applied to WHERE clauses and so a check for Aggrefs would be
+ * a waste of cycles; but be sure to also check contain_agg_clause() if you
+ * want to know about pseudo-constness in other contexts.
*/
bool
is_pseudo_constant_clause(Node *clause)