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Message Posted: Thu, 21 May 2009 @ 14:47:37 GMT


     
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Subj:   Column Order in Derived Table
 
From:   Goli, Srikanth

Hi -

Does Teradata optimizer need the select columns in a subquery to create a derived table to be in a specific order?

Assume the following -

     SEL ....
     FROM A
     Join (Sel  
             From B
             Where ..
          )C
     ON A.Col1 = B.Col1

Does it use the first column in the derived table B as the PI OR does the optimizer understand that regardless of location of B.Col1, that needs to be driver for distribution / hashing? I understand that with standalone "Create Tables As", this is a factor and that first column either be the PI column, or PI be explicitly specified. But with a derived table, where optimizer has access to statistics and query, does it still need the user specify the order?


Thanks.



     
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