How To Identify And Fix Inefficient Uses Of UNION

• How To Identify And Fix Inefficient Uses Of UNION

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  Carl Eric Johnson - click to view profile

  Description:

  The UNION and UNION ALL set operators are used to combine multiple intermediate result sets (typically from separate input sources) into a combined result. This is the most legitimate use of UNION. In the earlier years of DB2, however, before some of the more advanced features were added to the SQL syntax set, UNION was used for outer joins and for conditional processing. These less efficient uses of UNION need to be identified and replaced with their more efficient counterparts. This radio show presents what to look for and how to fix it.