Is your SQL optimized?

To check that your SQL is using the most optimized path, you should run EXPLAIN PLAN against the SQL.

This is a useful tip to help a DBA figure out if certain SQL has been optimized. It gives information in text and graphic form that shows how it's accessing tables and indexes. It also shows all the objects used in the plan and information about those objects such as tablesize, number of records, and more. It has been tested on DB2 UDB v6,7, 8.

Here are the steps to take:

  1. Put the SQL in a CLP file
  2. Run this command:
    db2 connect to <database>
    
  3. Run this command:
    db2 set current explain mode explain
    
  4. Run your SQL:
    db2 -vtf   *.CLP
    
  5. Run this command:
    db2exfmt -d <database> -1 -g TIC -o outputfile
    
This will put the explain plan in a text file that you can view and check out.

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This was first published in March 2003

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