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DB2 - Problembeschreibung

Problem IC66952 Status: Geschlossen

SERVER OPTION DB2_SELECT_SCALAR_SQ COULD CAUSE NICKNAME QUERY WITH A
SUBQUERY NOT TO BE PUSHED DOWN TO MVS SERVER

Produkt:
DB2 FOR LUW / DB2FORLUW / 970 - DB2
Problembeschreibung:
db2_select_scalar_sq is set to 'N' for MVS, VM, iSeries data 
sources by default. Federated queries involving subqueries in 
their select list will be blocked from being pushed down if this 
option was set to 'N'. E.g. 
sleect c1, (select max(c2) from NN) where from NN 
 
This query can not be fully pushed down to remote server if 
db2_select_scalar_sq is set to 'N', and hence a fully remote 
query plan can not be generated. 
 
In addition, this option can affect other queries's 
pushdownability, with a subquery in predicate of where-clause. 
The predicate has to be one with a constant and a subquery. E.g. 
select c1 from NN A where 1 >  (select max(B.c2) from NN B where 
B.c3 = A.c3) 
 
Note that, following query can be affect by this option too, 
although the subquery is in predicate with a column A.c2 instead 
of a constant: 
select c1 from NN A where A.c2  =  (select max(B.c2) from NN B 
where B.c3 = A.c3) and A.c2 < 1 
The reason is that, an implicit predicate "1 >  (select 
max(B.c2) from NN B where B.c3 = A.c3)" will be generated by 
DB2, deriving from the existing two predicates. The implicit 
predicate will then prevent the query from being pushed down.
Problem-Zusammenfassung:
**************************************************************** 
* USERS AFFECTED:                                              * 
* performance low                                              * 
**************************************************************** 
* PROBLEM DESCRIPTION:                                         * 
* none                                                         * 
**************************************************************** 
* RECOMMENDATION:                                              * 
* Setting db2_select_scalar_sq to 'Y' if remote server         * 
* supports a                                                   * 
* scalar subquery present in select list.                      * 
****************************************************************
Local-Fix:
Setting db2_select_scalar_sq to 'Y' if remote server supports a 
scalar subquery present in select list. In fact data sources 
like MVS V9 support it and this option should be set to 'Y' for 
them.
verfügbare FixPacks:
DB2 Version 9.7 Fix Pack 3 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 3a for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 4 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 5 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 6 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 7 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 8 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 9 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 9a for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 10 for Linux, UNIX, and Windows

Lösung
Workaround
keiner bekannt / siehe Local-Fix
Weitere Daten
Datum - Problem gemeldet    :
Datum - Problem geschlossen :
Datum - der letzten Änderung:
08.03.2010
25.09.2010
25.09.2010
Problem behoben ab folgender Versionen (IBM BugInfos)
Problem behoben lt. FixList in der Version
9.7.0.3 FixList
9.7.0.3 FixList