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Message Posted: Thu, 12 Aug 2004 @ 08:46:21 GMT


     
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Subj:   UNION And INSERT INTO
 
From:   Bach, Michael

Hello All

Taking an example of 2 SELECT statements combined by the UNION operator and being inserted into a table defined as CREATE SET.

The EXPLAIN will detail the elimination of duplicate rows in spool between the 2 SELECT statements.

My query to anyone who would know is whether this then removes the duplicate row checking process when the rows are inserted into the CREATE SET table? or would this step still take place because of the table definition.

The destination table would be empty and I'm aware there would be other ways of doing this. The query is purely to do with how the UNION and INSERT into CREATE SET table combine and whether the processing is clever enough to identify that duplicate row checks have already been performed within the UNION step.


Thanks in advance

Michael Bach,
AM Common Services
Group Data Warehouse - Service Continuity DBA



     
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