DB2 FOR LUW / DB2FORLUW / B10 - DB2

Data corruption is possible with MERGE statement using DISTINCT.
Statement should have returned SQL0788N.

Example:

create table S (C1 smallint, C2 varchar(10) );
create table T (C1 smallint, C2 varchar(10) );

insert into S values (1, 'A');
insert into S values (2, 'B');
insert into S values (3, 'C');
insert into S values (3, 'C2');
insert into S values (4, 'D');

insert into T values (1, 'A');
insert into T values (2, 'B');
insert into T values (3, 'C');
insert into T values (4, 'D');

db2 => merge into T using (select distinct c1, c2 from S) S
on T.C1 = S.C1
when matched then update set T.C2 = T.C2 || '-' || S.C2
DB20000I  The SQL command completed successfully.

Both target rows with C1=3 are updated.
The above statement should get error -788.

db2 => select * from T;

C1     C2
------ ----------
     1 A-A
     2 B-B
     3 C-C2
     4 D-D

  4 record(s) selected.

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* USERS AFFECTED:                                              *
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* PROBLEM DESCRIPTION:                                         *
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* RECOMMENDATION:                                              *
* Upgrade to Db2 11.1 Mod 4 Fixpack 4 iFix 001 or higher       *
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If the DISTINCT clause is not strictly necessary, remove it.
Otherwise, ensure that each column in the source table-reference
is also included in the MERGE search condition, e.g. for the
example above, add predicate T.C2=S.C2:

merge into T using (select distinct c1, c2 from S) S
on T.C1 = S.C1 and T.C2 = S.C2
when matched then update set T.C2 = T.C2 || '-' || S.C2;

not known / see Local fix

forerunner  : IT27705 
follow-up : 

Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :

10.01.2019
07.03.2019
08.03.2019