IT17506: IN DB2 DPF, POSSIBLE WRONG RESULT WHEN OUTER JOIN PREDICATE COL1=COL2 AND BOTH COLUMNS ARE FROM THE OUTER TABLE

DB2 Version 10.1 Fix Pack 6 for Linux, UNIX, and Windows

APAR status

• Closed as program error.

Error description

• DB2 can return wrong query result when all of the following
  conditions are satisfied
  
  1. DPF (Data Partitioning Feature) environment.
  2. The query has a outer join, and the outer join has a
  predicate of the form COLUMN1=COLUMN2, where both columns are
  from the outer table.
  3. Either DB2COMPOPT=OJLOCALPRDPLANNING is set, or the
  NULL-producing side of the outer join is a CSE (Common
  SubExpression), UNION, GROUP-BY, or another outer join.
  4. The query has a key requirement or order requirement on one
  of the columns in the COLUMN1=COLUMN2 predicate.
  
  For example:
  
  The following query can possibly produce a wrong result in DPF
  environment, because the query has an outer join predicate of
  TT.T1_C1 = TT.T1_C2, the NULL-producing side of the outer join
  is another outer join, and the query requires "DISTINCT
  TT.T1_C2"
  
  SELECT DISTINCT TT.T1_C2 FROM T1 TT LEFT OUTER JOIN
  (SELECT T2.T2_C4 FROM T2 FULL OUTER JOIN T1 ON T1.T1_C1 =
  T2.T2_C2) TT2 on TT.T1_C1 = TT.T1_C2
  
  The following query can possibly produce a wrong result in DPF
  environment and when DB2COMPOPT=OJLOCALPRDPLANNING is set,
  because the query has an outer join predicate of
  T1.T1_C1=T1.T1_C2, and the query requires "ORDER BY TT.T1_C2"
  
  SELECT * FROM T2 TT1, (SELECT * FROM T1 LEFT JOIN T2 on
  T1.T1_C1=T1.T1_C2 ) TT
  WHERE TT1.T2_C4 = TT.T1_C1
  ORDER BY TT.T1_C2
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * ALL                                                          *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to DB2 10.1 Fix Pack 6                               *
  ****************************************************************
  

Problem conclusion

• First fixed in DB2 10.1 Fix Pack 6
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  IT17458

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  DB2 FOR LUW

• Fixed component ID

  DB2FORLUW

Applicable component levels

• RA10 PSN UP

     FIX