Comments on: Is it possible on iSeries that an index is defined keeping in mind an sql select criteriea however when the queryis run this index does not get used. http://itknowledgeexchange.techtarget.com/itanswers/is-it-possible-on-i-series-that-an-index-is-defined-keeping-in-mind-an-sql-select-criteriea-however-when-the-queryis-run-this-index-does-not-get-used/ Thu, 20 Jun 2013 11:12:44 +0000 hourly 1 By: tomliotta http://itknowledgeexchange.techtarget.com/itanswers/is-it-possible-on-i-series-that-an-index-is-defined-keeping-in-mind-an-sql-select-criteriea-however-when-the-queryis-run-this-index-does-not-get-used/#comment-85771 tomliotta Fri, 24 Dec 2010 02:41:53 +0000 #comment-85771 Yes, it is possible. It is even likely.

Most indexes are not used in most queries. You might have ten indexes over a table, but usually no more than one is used; and sometimes none are used. You might have an index over a column and reference the column in a WHERE or ORDER BY clause, and the index still might not be used.

To find out why an index is used or not used, follow Phil’s advice. Run the query in debug. SQL will log messages about the choices it makes when debug is active.

iSeries Navigator also has a number of options that can help analyze how queries are run. Drill down into Databases and right-click on your system’s database name. Select ‘Run SQL Scripts…’. Review the menu options to see what’s available. Pay special attention to the VisualExplain menu item.

Tom

]]> By: murrayinfosys http://itknowledgeexchange.techtarget.com/itanswers/is-it-possible-on-i-series-that-an-index-is-defined-keeping-in-mind-an-sql-select-criteriea-however-when-the-queryis-run-this-index-does-not-get-used/#comment-85726 murrayinfosys Thu, 23 Dec 2010 23:18:45 +0000 #comment-85726 JohnsonMumbai -
IBM has what I would call a Query Analyser. If you are able to, run the job in Debug mode with full job loging. It should tell you why it took the path that it did. I do this all the time with RPG/SQL programs. It can make a HUGE difference.

Phil

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