IT30466: DB2 MAY PRODUCE INCORRECT RESULTS WHEN EXECUTING QUERIES CONTAINING JOINS WITH DIFFERING FLOATING-POINT PRECISIONS

APAR status

• Closed as program error.

Error description

• Db2 may produce incorrect results when executing a query
  containing the following properties:
  
  - The query contains an inner join.
  - The join columns for the inner join have different data types
  but are both floating-point data types.
  - The query contains a local predicate with either operand as
  one of the join columns.
  - The other operand of the local predicate has a larger
  precision than the join column that isn't referenced in the
  local predicate
  - The precision of the join column used in the local predicate
  is equal to or smaller than the precision of the other join
  column
  
  For example:
  
  CREATE TABLE T1 (DF16 DECFLOAT(16));
  CREATE TABLE T2 (DEC8 DECIMAL(8));
  
  INSERT INTO T1 VALUES 1, 2;
  INSERT INTO T2 VALUES 1, 2;
  
  SELECT T2.DEC8 FROM T1 INNER JOIN T2 ON T1.DF16 = T2.DEC8 WHERE
  T2.DEC8 = CAST(1 AS DECIMAL(20));
  
  Expected Results:
  
  DEC16
  ----------
          1.
  
    1 record(s) selected.
  
  Actual Results:
  
  DEC16
  ----------
          1.
          2.
  
    2 record(s) selected.
  

Local fix

• If possible, rewrite the local predicate so that both operands
  use the same (or smaller) precision as the join column that
  isn't referenced in the local predicate. For example:
  
  SELECT T2.DEC8 FROM T1 INNER JOIN T2 ON T1.DF16 = T2.DEC8 WHERE
  T2.DEC8 = CAST(1 AS DECIMAL(16));
  
  In this example, the constant operand of the local equality
  predicate has been changed to a DECIMAL(16) to match the
  precision of column DF16 (which is a DECFLOAT(16)).
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * DB2 may produce incorrect results when executing queries     *
  * containing joins with differing floating-point precisions    *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to version v11.1m4fp5                                *
  ****************************************************************
  

Problem conclusion

• This issue will be fixed in db2 V11.1m4fp5
  

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:

  IT30467 IT30469

Fix information

• Fixed component name

  DB2 FOR LUW

• Fixed component ID

  DB2FORLUW

Applicable component levels