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 |
