DB2 FOR LUW / DB2FORLUW / A50 - DB2

Queries that contain complex OR predicates may experience poor 
cardinality estimation and a poorly performing access plan may 
be generated. The OR predicate must 
- reference multiple columns 
- each subterm of the OR contains references to some of the same 
columns 
- for a given column the predicate in each OR subterm is 
different 
 
For example 
 
  ((ca_country = 'United States' and 
    ca_state in ('KY', 'GA', 'NM') and 
    ss_net_profit between 100 and 200) 
 or 
   (ca_country = 'United States' and 
    ca_state in ('MT', 'OR', 'MT') and 
    ss_net_profit between 150 and 300) 
 or 
   (ca_country = 'United States' and 
    ca_state in ('IN', 'WI', 'MO') and 
    ss_net_profit between 50 and 250)) 
 
Each subterm of the OR predicate contains a reference to 
ca_country, ca_state and ss_net_profit. For the columns ca_state 
and ss_net_profit, the actual predicate referencing these 
columns is different in each branch. 
 
Such an OR predicate may be susceptible to incorrect filter 
factor estimation, 
using the db2exfmt output you may see predicates with the 
SELECTIVITY 1.0 attribute. 
 
(Q5.SS_SALES_PRICE >= +50.00 SELECTIVITY 1.000000) AND 
(Q5.SS_SALES_PRICE <= +300.00 SELECTIVITY 1.000000) 
 
Using some test queries you should validate whether the 
cardinality 
of lower operators in the plan is accurate.

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* USERS AFFECTED:                                              * 
* ALL                                                          * 
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* PROBLEM DESCRIPTION:                                         * 
* See Error Description                                        * 
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* RECOMMENDATION:                                              * 
* Upgrade to DB2 LUW version 10.5 fixpak 4.                    * 
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DB2 Cancun Release 10.5.0.4 (also known as Fix Pack 4) for Linux, UNIX, and Windows
 DB2 Version 10.5 Fix Pack 9 for Linux, UNIX, and Windows
 

First fixed in DB2 LUW version 10.5 fixpak 4.

not known / see Local fix

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

14.05.2014
08.09.2014
08.09.2014