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From "A B (JIRA)" <derby-...@db.apache.org>
Subject [jira] Created: (DERBY-1681) Regression (wrong results): Join predicate can be ignored for left-most child in a chain of nested unions.
Date Fri, 11 Aug 2006 22:03:13 GMT
Regression (wrong results): Join predicate can be ignored for left-most child in a chain of
nested unions.
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                 Key: DERBY-1681
                 URL: http://issues.apache.org/jira/browse/DERBY-1681
             Project: Derby
          Issue Type: Bug
          Components: SQL
    Affects Versions: 10.1.3.1, 10.1.3.0, 10.2.0.0
            Reporter: A B
             Fix For: 10.2.0.0


If Derby chooses to do a join between two FromTables and the right table is a chain of UNIONs,
then the optimizer may choose to push the join predicate (if provided) down into the UNION
and to both children of every UNION in the chain.  But if the predicate cannot be pushed to
the children of any of the UNIONs (except the top-level one)  the predicate can end up being
ignored altogether with respect to that UNION's children.  The result is that query execution
can return rows that do not satisfy the predicate.

This is a regression introduced in 10.1.2.4 and thus it affects 10.1.3 and 10.2.  I came across
this while tracing through code for DERBY-1633.

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