[teiid-issues] [JBoss JIRA] (TEIID-1991) GROUP BY pushdown into subselect of UNIONs

[Mark Addleman (JIRA)]

Mark Addleman created TEIID-1991:
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             Summary: GROUP BY pushdown into subselect of UNIONs
                 Key: TEIID-1991
                 URL: https://issues.jboss.org/browse/TEIID-1991
             Project: Teiid
          Issue Type: Bug
          Components: Query Engine
    Affects Versions: 7.7
            Reporter: Mark Addleman
            Assignee: Steven Hawkins
         Attachments: plan.txt

If have a query of the form
SELECT a FROM (
   SELECT a FROM (
       SELECT a FROM ds.t1
   ) u
) t GROUP BY a

Teiid correctly optimizes the inner SELECT to SELECT 1 FROM ds.t1.  However, if the inner subselect is a union:
SELECT a FROM (
   SELECT a FROM (
       SELECT a FROM ds.t1 UNION
       SELECT a FROM ds.t2
   ) u
) t GROUP BY a
			
Teiid does not optimize to 
   SELECT 1 FROM ds.t1 UNION
   SELECT 1 FROM ds.t2
as I would expect.

See attached plan

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