Where to put the Where Clause

This should be a simple question...

I am using UNION to join multiple tables with the same columns. At the end of the my UNION I am aliasing the whole thing as a tableX. After that I have a WHERE statement and a GROUP statement. Efficiency is of great importance! I want to know if it makes a difference from an effeciency standpoint if I repeat the WHERE and GROUP clause with each table in the union, or if I just have it at the end after the alais.
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MapleMaleAsked:
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BrandonGalderisiConnect With a Mentor Commented:
If you put your where clause and group by in each part of the union, then the # of records returned will be lower in each part of the union.  Also, your where and group by can utilize the indexes of the table.
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Guy Hengel [angelIII / a3]Billing EngineerCommented:
the WHERE clause should be per each SELECT.
SELECT ...
  FROM ...
 WHERE ...
 GROUP BY ...
UNION ALL
SELECT ...
  FROM ...
 WHERE ... 
 GROUP BY ...

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