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Message Posted: Wed, 05 May 2004 @ 19:56:34 GMT


     
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Subj:   Re: Collect Stats on Indexes versus Multi-Column
 
From:   Dieter Noeth

Claybourne Barrineau wrote:

     TableA
     ColA
     ColB
     ColC
     ColD
     UPI = ColA
     Index (ColB, ColC)
  Are the following 2 statements equivalent to the RDBMS?  


  1)Collect Stats on TableA Index (ColB, ColC);  


  2)Collect Stats on TableB Column (ColB, ColC);  


  From an 'Explain' point of view, they look identical.  



There's a difference:

You can drop and recreate that index without losing statistics (similar to a single column index), if you collect on multi-column, because those statistics are stored as a pseudo-index (with indextype 'M') in dbc.indexes.


Dieter



     
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