[teiid-issues] [JBoss JIRA] (TEIID-1991) GROUP BY pushdown into subselect of UNIONs
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https://issues.jboss.org/browse/TEIID-1991?page=com.atlassian.jira.plugin...
]
Mark Addleman commented on TEIID-1991:
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When there is a single SELECT in the inline view
SELECT u.datamart_name
FROM (
SELECT 'abc' AS DATAMART_NAME, a.evttypecode
FROM SECURITY_DM_DATACOM_DEV_R140_XE59_CMGRD1.ADMACCOUNT AS a
) AS u
GROUP BY u.datamart_name
It appears that Teiid understands it only needs to know if there is *any* data coming from
the ADMACCOUNT table, so it issues SELECT 1 FROM
SECURITY_DM_DATACOM_DEV_R140_XE59_CMGRD1.ADMACCOUNT instead.
I would expect Teiid to apply the same optimization if the inline view contained a UNION.
GROUP BY pushdown into subselect of UNIONs
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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: efficient_rewrite.txt, plan.txt, plan.txt, simplified_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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