IT35118: POSSIBLE WRONG RESULT WITH ALWAYS-FALSE PRED OR EXISTS PRED

Db2 Version 11.1 Mod 4 Fix Pack 6 for Linux, UNIX, and Windows
Db2 Version 11.1 Mod 4 Fix Pack 6 for Linux, UNIX, and Windows

APAR status

• Closed as program error.

Error description

• When a query has always-false predicates or EXISTS predicates,
  we may get wrong results. More specifically, we may get more
  rows returned than anticipated.
  
  Another example with always-false predicates:
  
       create table t1 (c1 int);
       create table t2 (c1 int);
  
       insert into t1 values (5);
       insert into t2 values (5), (5);
  
       -- Bad query with "always false" predicate, should return 1
  row, returns 2
       select * from t1
       where ((t1.c1 < 1 and t1.c1 > 2 )    -- Always false
  predicate
               or
              (exists(select * from t2 where t2.c1=t1.c1)));
  
       C1
       -----------
                 5
                 5
  
         2 record(s) selected.
  
       -- Same query without "always false" predicate, correctly
  returns 1 row
       select * from t1
       where exists(select * from t2 where t2.c1=t1.c1);
  
       C1
       -----------
                 5
  
         1 record(s) selected.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All                                                          *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to Db2 version 11.1.4.6                              *
  ****************************************************************
  

Problem conclusion

• Fixed in Db2 version 11.1.4.6
  

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:

Fix information

• Fixed component name

  DB2 FOR LUW

• Fixed component ID

  DB2FORLUW

Applicable component levels

• RB10 PSN

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