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  • Subject: Re: SQL CTE of a UNION kills performance
  • From: Buck Calabro <kc2hiz@xxxxxxxxx>
  • Date: Wed, 29 Aug 2018 11:12:24 -0400
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On 8/28/2018 7:03 PM, Charles Wilt wrote:
If you're using Run SQL Scripts you can change to *ALLIO in the JDBC
connection config.

I can confirm that in fact, *ALLIO as an optimisation goal causes the
non-CTE to run as slowly as the CTE does. Good diagnostic, thanks.

The view (my ultimate goal) is used in stored procedures that are called
by various ODBC-centric applications as well as Good Old Fashioned
SQLRPGLE. So changing the JDBC configuration won't help out there.

I tried OPTIMIZE FOR 1 ROWS but the 7.3 TR4 optimizer doesn't use that
hint to optimise the CTE-based UNIONs. What ultimately worked for the
issue was to extract the CTE out into its own VIEW, and SELECT ... FROM
the view.


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