IT21948: DB2 MAY RETURN WRONG RESULTS WITH ORACLE COMPATIBILITY AND SUBSTR

Db2 Version 11.1 Mod2 Fix Pack2 iFix002 for Linux, UNIX, and Windows
Db2 Version 11.1 Mod 3 Fix Pack 3 for Linux, UNIX, and Windows
Db2 Version 11.1 Mod3 Fix Pack3 iFix001 for Linux, UNIX, and Windows
Db2 Version 11.1 Mod3 Fix Pack3 iFix002 for Linux, UNIX, and Windows

APAR status

• Closed as program error.

Error description

• DB2 may return wrong results when all the following conditions
  are met:
  -The database has oracle compatibility
  (DB2_COMPATIBILITY_VECTOR=ORA) mode enabled.
  -The SELECT query being issued contains a relational operator
  predicate with SUBSTR.
  -The string argument to SUBSTR is from a table that has an index
  on that column.
  -The other operand of the relational operator is a literal.
  
  This forces the optimizer to perform an index scan using only
  the
  start/stop predicates. The index scan LOLEPOP does not contain
  the SUBSTR predicate, only the start/stop preds.
  
  Example:
  
  create table t (v VARCHAR(128));
  create index i on t(v);
  insert into t values 'PT1', 'PT10';
  
  select v from t where substr(v, 1, 20) = cast('PT1' as
  VARCHAR(20));
  
  The above query returns two rows ('PT1', 'PT10') when we should
  only
  be returning one ('PT1').
  
  The expected result (one row) is returned by the following:
  
  select v from t where v = cast('PT1' as VARCHAR(20));
  

Local fix

• Workaround:
  
  Replace the literal with a table column or variable.
  Continuing with the example above:
  
  create variable myvar char(3) default 'PT1';
  select * from test where substr(v, 1, 20) = myvar;
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * ALL                                                          *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to Db2 11.1 Mod 2 Fix Pack 2 iFix002 or higher       *
  ****************************************************************
  

Problem conclusion

• First fixed in Db2 11.1 Mod 2 Fix Pack 2 iFix002
  

Temporary fix

Comments

APAR Information

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

  IT21760

• 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