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DB2 - Problem description

Problem IT04410 Status: Closed

DB2 OPTIMIZER MIGHT CHOOSE SUBOPTIMAL ACCESS PLAN FOR SELECT STATEMENT WITH
VALUES CLAUSE

product:
DB2 FOR LUW / DB2FORLUW / 970 - DB2
Problem description:
DB2 optimizer might choose suboptimal access plan for SELECT 
statement that defines a temporary table by using VALUES clause. 
 
For example, consider the following query: 
   SELECT T1.C2, T1.C4, T1.C5 
   FROM   T1, 
          ( SELECT * 
            FROM ( VALUES  CAST ( ? AS VARCHAR(150) ), 
                   ?, ?, ?, ?, ?, ?, ?, ?, ?, 
                   ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, 
                   ?, ?, ?, ?, ?, ?, ?, ?, ?, ? 
          ) AS T2_TMP ( C1 ) GROUP BY C1 ) AS T2 
   WHERE  T1.C1 = ? AND 
          T1.C2 = T2.C1 AND 
          T1.C3 = ? AND 
          T1.C4 IN ( ?, ? ) 
 
There is an index on columns ( C1, C2, C3, C4, C5 ). 
 
In this case, if the join predicate T1.C2 = T2.C1 is very 
selective, 
then one of the best access plans to execute this query is 
NLJOIN 
plan with T1 on inner side (RHS) and T2 on outer side (LHS). 
 
The query optimizer may not choose the above mentioned NLJOIN 
plan. 
For example, a suboptimal plan that applies T1.C4 IN ( ?, ? ) 
predicate 
as in2join could be chosen.
Problem Summary:
**************************************************************** 
* USERS AFFECTED:                                              * 
* All                                                          * 
**************************************************************** 
* PROBLEM DESCRIPTION:                                         * 
* See Error Description                                        * 
**************************************************************** 
* RECOMMENDATION:                                              * 
* Upgrade to DB2 Version 9.7 Fix Pack 11.                      * 
****************************************************************
Local Fix:
You can force the good NLJOIN plan by using optimization 
profile.
Solution
First fixed in DB2 Version 9.7 Fix Pack 11.
Workaround
not known / see Local fix
Timestamps
Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :
16.09.2014
19.10.2015
19.10.2015
Problem solved at the following versions (IBM BugInfos)
9.7.FP11
Problem solved according to the fixlist(s) of the following version(s)
9.7.0.11 FixList
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