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DB2 - Problem description

Problem IC63329 Status: Closed

Two or more outer joins containing f(NULL) that returns non-null value may
return incorrect results

product:
DB2 FOR LUW / DB2FORLUW / 910 - DB2
Problem description:
SQL statement that contains two or more outer joins with the 
predicate of the first ON clause containing expressions that 
could change the null value of the left side of the LEFT outer 
join to a non-null value may return incorrect results. 
 
Example: 
 
WITH A(A1) as (values 1), 
        B(B1) as (values cast(NULL as INTEGER)), 
        C(C1) as (values 1) 
SELECT A1,B1,C1 
FROM   A LEFT JOIN (B LEFT JOIN C ON COALESCE(B1,1)=C1) ON 
A1=B1; 
 
The above statement hits this APAR because 
1. There are two outer joins. 
2. The expression in the first ON clause, COALESCE(B1,1)=C1 
could change the value of NULL of B1 to a non-null value. 
 
The correct result for the above statement is 
 
A1          B1          C1 
----------- ----------- ----------- 
          1           -           - 
 
An example of a SQL statement that does NOT hit this APAR is 
 
WITH A(A1) as (values 1), 
        B(B1) as (values cast(NULL as INTEGER)), 
        C(C1) as (values 1) 
SELECT A1,B1,C1 
FROM   A LEFT JOIN (B LEFT JOIN C ON COALESCE(B1,1)=C1) AND 
B1=C1 ON A1=B1; 
 
Even though, the COALESCE expression exists, the addition 
expression B1=C1, which return NULL if B1 is NULL, will safe 
guard this statement to not return incorrect results.
Problem Summary:
USERS AFFECTED 
 
All 
 
PROBLEM DESCRIPTION 
 
see ERROR DESCRIPTION 
 
PROBLEM SUMMARY 
 
see ERROR DESCRIPTION
Local Fix:
available fix packs:
DB2 Version 9.1 Fix Pack 9  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 10  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 11  for Linux, UNIX and Windows
DB2 Version 9.1 Fix Pack 12  for Linux, UNIX and Windows

Solution
The complete fix for this problem first appears in DB2 UDB 
Version 9.1 FixPak 9.
Workaround
not known / see Local fix
Timestamps
Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :
22.09.2009
14.04.2010
14.04.2010
Problem solved at the following versions (IBM BugInfos)
9.0.,
9.1.
Problem solved according to the fixlist(s) of the following version(s)
9.1.0.9 FixList
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