DB2 FOR LUW / DB2FORLUW / B10 - DB2

If a query contains a sub-query with SELECT DISTINCT together
with other complex operations such as OUTER JOIN and UNION ALL,
the query performance might be regressed.

Example query:

SELECT t3.c4
FROM (SELECT t1.c2 FROM t1 LEFT OUTER JOIN t2 ON t1.c1 = t2.c1)
AS v1(c2), t3
WHERE v1.c2 = t3.c1 AND t3.c3 IN (SELECT DISTINCT c3 FROM t3
WHERE c2 = 100)

In v11.1.3, the SELECT DISTINCT sub-query is merged into the
outer query block and DISTINCT is executed as part of the outer
SELECT clause.

Prior to V11.1.3, the sub-query is not merged and DISTINCT is
executed as part of the sub-query.

****************************************************************
* USERS AFFECTED:                                              *
* ALL                                                          *
****************************************************************
* PROBLEM DESCRIPTION:                                         *
* See Error Description                                        *
****************************************************************
* RECOMMENDATION:                                              *
* Upgrade to Db2 11.1 Mod 4 Fixpack 5 or higher                *
****************************************************************

Workaround: Apply the following registry setting using the
optimization guideline to the affected queries:

/* 
   
        
   
 */

not known / see Local fix

Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :

04.03.2019
16.01.2020
16.01.2020