IT28638: DB2 MAY PRODUCE INCORRECT RESULTS FOR HSJN WITH PREDICATE THAT HAS CASE(COALESCE) AND NLJN OR ZZJOIN ON THE OUTER

APAR status

• Closed as program error.

Error description

• DB2 MAY PRODUCE INCORRECT RESULTS FOR HSJN WHEN
  - HSJN HAS COMPLEX PREDICATE THAT HAS CASE ( COALESCE )
  - HSJN HAS NLJN OR ZZJOIN ON THE OUTER
  - INTERNAL OPTIMIZATION IS APPLIED
  
  Example of the Complex Predicate in HSJN from the Plan that
  could produce wrong results:
  
  Predicate Text:
  --------------
  (Q8.C1 =
  CASE
  WHEN (Q1.C2 = 'X')
  THEN COALESCE(Q1.C3, 'Y')
  WHEN NOT(Q1.C4 IN ('A', 'B'))
  THEN
  CASE
  WHEN UPPER(COALESCE(Q2.C5, 'D')) IN ('E', 'F', 'G')
  THEN 'H'
  WHEN (UPPER(COALESCE(Q2.C5, 'D')) = 'K')
  THEN 'L'
  ELSE COALESCE(Q2.C5, 'D') END
  ELSE COALESCE(Q2.C5, 'D') END)
  
  Example of HSJN with NLJN on the outer:
  
                                              101225
                                                HSJN
                                                ( 6)
                                               552757
                                       /------/      \----\
                                 101225                       46
  
                                  NLJN                      ISCAN
  
                                  ( 7)                        (22)
  
                                 552653                   ...
                                /      \
                           101224        1
                            SCAN       ISCAN
                            ( 8)         (21)
                           548163    ...
                             |
  ...
  

Local fix

• db2set DB2_TCG_DEFAULT_OPTIONS="set disable_pushdown on"
  instance restart is needed
  Static packages need  to be rebound.
  

Problem summary

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

Problem conclusion

• First fixed in Db2 11.1 Mod 4 Fixpack 5
  

Temporary fix

Comments

APAR Information

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

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

  IT30005 IT30006

Fix information

• Fixed component name

  DB2 FOR LUW

• Fixed component ID

  DB2FORLUW

Applicable component levels