*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.167 2004/12/31 22:00:04 pgsql Exp $
+ * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.168 2005/03/01 00:24:52 tgl Exp $
*
*-------------------------------------------------------------------------
*/
RestrictInfo *rinfo);
static Oid indexable_operator(Expr *clause, Oid opclass,
bool indexkey_on_left);
-static bool pred_test_recurse_pred(Expr *predicate, List *restrictinfo_list);
static bool pred_test_restrict_list(Expr *predicate, List *restrictinfo_list);
static bool pred_test_recurse_restrict(Expr *predicate, Node *clause);
+static bool pred_test_recurse_pred(Expr *predicate, Node *clause);
static bool pred_test_simple_clause(Expr *predicate, Node *clause);
static Relids indexable_outerrelids(RelOptInfo *rel, IndexOptInfo *index);
static Path *make_innerjoin_index_path(Query *root,
* Recursively checks whether the clauses in restrictinfo_list imply
* that the given predicate is true.
*
- * This routine (together with the routines it calls) first breaks down
- * the predicate to its constituent AND/OR elements, then similarly
- * breaks down the restriction clauses to AND/OR elements in an effort
- * to prove that each predicate element is implied. The top-level
- * List structure of each list corresponds to an AND list.
+ * This routine (together with the routines it calls) iterates over
+ * ANDs in the predicate first, then breaks down the restriction list
+ * to its constituent AND/OR elements, and iterates over ORs
+ * in the predicate last. This order is important to make the test
+ * succeed whenever possible. --Nels, Jan '93
+ *
+ * For example, a restriction (a OR b) certainly implies a predicate
+ * (a OR b OR c), but no one element of the predicate is individually
+ * implied by the restriction. By expanding the predicate ORs last
+ * we are able to prove that the whole predicate is implied by each arm
+ * of the restriction. Conversely consider predicate (a AND b) with
+ * restriction (a AND b AND c). This should be implied but we will
+ * fail to prove it if we dissect the restriction first.
+ *
+ * The top-level List structure of each list corresponds to an AND list.
+ * We assume that canonicalize_qual() has been applied and so there
+ * are no explicit ANDs immediately below the top-level List structure.
+ * (If this is not true we might fail to prove an implication that is
+ * valid, but no worse consequences will ensue.)
*/
bool
pred_test(List *predicate_list, List *restrictinfo_list)
return false; /* no restriction clauses: the test must
* fail */
+ /* Take care of the AND semantics of the top-level predicate list */
foreach(pred, predicate_list)
{
/*
* if any clause is not implied, the whole predicate is not
* implied.
*/
- if (!pred_test_recurse_pred(lfirst(pred), restrictinfo_list))
+ if (!pred_test_restrict_list(lfirst(pred), restrictinfo_list))
return false;
}
return true;
}
-/*
- * pred_test_recurse_pred
- * Does the "predicate inclusion test" for one conjunct of a predicate
- * expression. Here we recursively deal with the possibility that the
- * predicate conjunct is itself an AND or OR structure.
- */
-static bool
-pred_test_recurse_pred(Expr *predicate, List *restrictinfo_list)
-{
- List *items;
- ListCell *item;
-
- Assert(predicate != NULL);
- if (or_clause((Node *) predicate))
- {
- items = ((BoolExpr *) predicate)->args;
- foreach(item, items)
- {
- /* if any item is implied, the whole predicate is implied */
- if (pred_test_recurse_pred(lfirst(item), restrictinfo_list))
- return true;
- }
- return false;
- }
- else if (and_clause((Node *) predicate))
- {
- items = ((BoolExpr *) predicate)->args;
- foreach(item, items)
- {
- /*
- * if any item is not implied, the whole predicate is not
- * implied
- */
- if (!pred_test_recurse_pred(lfirst(item), restrictinfo_list))
- return false;
- }
- return true;
- }
- else
- return pred_test_restrict_list(predicate, restrictinfo_list);
-}
-
-
/*
* pred_test_restrict_list
- * Does the "predicate inclusion test" for one element of a predicate
+ * Does the "predicate inclusion test" for one AND clause of a predicate
* expression. Here we take care of the AND semantics of the top-level
* restrictinfo list.
*/
/*
* pred_test_recurse_restrict
- * Does the "predicate inclusion test" for one element of a predicate
+ * Does the "predicate inclusion test" for one AND clause of a predicate
* expression. Here we recursively deal with the possibility that the
* restriction-list element is itself an AND or OR structure; also,
- * we strip off RestrictInfo nodes to find bare predicate expressions.
+ * we strip off RestrictInfo nodes to find bare qualifier expressions.
*/
static bool
pred_test_recurse_restrict(Expr *predicate, Node *clause)
}
return false;
}
+ else
+ return pred_test_recurse_pred(predicate, clause);
+}
+
+
+/*
+ * pred_test_recurse_pred
+ * Does the "predicate inclusion test" for one conjunct of a predicate
+ * expression. Here we recursively deal with the possibility that the
+ * predicate conjunct is itself an AND or OR structure.
+ */
+static bool
+pred_test_recurse_pred(Expr *predicate, Node *clause)
+{
+ List *items;
+ ListCell *item;
+
+ Assert(predicate != NULL);
+ if (or_clause((Node *) predicate))
+ {
+ items = ((BoolExpr *) predicate)->args;
+ foreach(item, items)
+ {
+ /* if any item is implied, the whole predicate is implied */
+ if (pred_test_recurse_pred(lfirst(item), clause))
+ return true;
+ }
+ return false;
+ }
+ else if (and_clause((Node *) predicate))
+ {
+ items = ((BoolExpr *) predicate)->args;
+ foreach(item, items)
+ {
+ /*
+ * if any item is not implied, the whole predicate is not
+ * implied
+ */
+ if (!pred_test_recurse_pred(lfirst(item), clause))
+ return false;
+ }
+ return true;
+ }
else
return pred_test_simple_clause(predicate, clause);
}
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