unknown 5c4e64a574 MWL#89 ...

Fixed query plans with loose index scan degraded into index scan.

Analysis:
With MWL#89 subqueries are no longer executed and substituted during
the optimization of the outer query. As a result subquery predicates
that were previously executed and substituted by a constant before
the range optimizer were present as regular subquery predicates during
range optimization. The procedure check_group_min_max_predicates()
had a naive test that ruled out all queries with subqueries in the
WHERE clause. This resulted in worse plans with MWL#89.

Solution:
The solution is to refine the test in check_group_min_max_predicates()
to check if each MIN/MAX argument is referred to by a subquery predicate.

2011-01-18 00:53:41 +02:00

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