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Why OR extremely slows down the query?

P: 1
I have a query, which takes about 4 seconds to execute
Expand|Select|Wrap|Line Numbers
  1. SELECT wq.nr
  2. FROM wq, wq_xml
  3. WHERE wq.nr = wq_xml.nr
  4. AND wq.type = 2
  5. AND SUBSTR(wq_xml.xml_data, POSSTR(SUBSTR(wq_xml.xml_data, 1, 200), 'bagmeGd=') IN ('41', '42', '43', '44', '45', '47')
  6. AND state = 91
If I change the last row to AND (state = 91 OR state = 93) it takes more than 10 minutes to execute. What is wrong with this query?
I have DB2 v.8.1.11.973 installed on Win XPSP2 machine
Sep 18 '07 #1
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1 Reply


docdiesel
Expert 100+
P: 297
Hi Ovartomortes,

use the DB2 explain function ( http://publib.boulder.ibm.com/infoce...n/c0005135.htm ). It shows you graphically how DB2 is working on a statement, if/how it's using indexes, joining tables etc. It will show you the difference you're looking for.

You also might try "AND state in (91,93)" and see the influence.

Regards, Bernd
Sep 18 '07 #2

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