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Status Not under consideration
Workspace Db2 for z/OS
Created by Guest
Created on Nov 11, 2019

RELATED IDEAS

The rewrite from non-correlated sub-select to a correlated sub-select should happen in additional cases

This was submitted initially as a case with ID TS002883559.

The following query is not rewritten by Db2 (from non-correlated to correlated):

 

SELECT *
FROM
PDBR111.VLCR004_NODELS TLCRTABLE0X0_ LEFT OUTER JOIN
(SELECT *
FROM PDBR111.TLCR002 A
WHERE A.CLM_NUM IN
(SELECT B.CLM_NUM FROM PDBR111.TLCR004 B
WHERE
B.CLM_POL_STUS_CDE <> 'J' )) TLCRTABLE0X1_
ON TLCRTABLE0X0_.CLM_NUM=TLCRTABLE0X1_.CLM_NUM
WHERE
TLCRTABLE0X0_.CLM_NUM=? ;

 

Applying a manual rewrite that follows will make the query run over 1000x faster:

 

SELECT *
FROM
PDBR111.VLCR004_NODELS TLCRTABLE0X0_ LEFT OUTER JOIN
(SELECT *
FROM PDBR111.TLCR002 A
WHERE EXISTS (
SELECT 1 FROM PDBR111.TLCR004 B
WHERE A.CLM_NUM = B.CLM_NUM
AND B.CLM_POL_STUS_CDE <> 'J' )) TLCRTABLE0X1_
ON TLCRTABLE0X0_.CLM_NUM=TLCRTABLE0X1_.CLM_NUM
WHERE
TLCRTABLE0X0_.CLM_NUM=? ;

 

Applying a manual rewrite that follows will make the query run over 1000x faster:

 

Many times, manually rewriting a query becomes difficult.  If the optimization of the query would do this, it could make queries like this one run far faster without a manual rewrite of the query.

 

This would help us with Db2 performance.

Needed by Date Aug 1, 2020
  • Admin
    Janet Figone
    Reply
    |     Dec 30, 2020

    Thank you for submitting this Db2 for z/OS enhancement request. We have reviewed this request and believe it may a good candidate for the Db2 for z/OS product. However, it is not in our current roadmap and we are unable to deliver it within the next 24 months. Therefore, unfortunately, we will not be implementing this Idea.

    We appreciate your input to the Db2 for z/OS development team. We also hope that you will continue to submit ideas for improvements as customer feedback is a key component to shaping the future direction of Db2 for z/OS.

    Sincerely,

    Db2 for z/OS Team

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