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Message Posted: Tue, 08 Dec 2009 @ 16:22:33 GMT


     
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Subj:   Re: Theoretical collection over collecting stats
 
From:   Roth, David W

Continuing on, a secondary index "might" make the query run faster if it can identify specific rows (and corresponding blocks) to pull based on the selectivity of the value; lower is better.

So for a table with a column having 3 values where value a is 80% of rows and values b & c are 10% respectively, the optimizer might use the secondary index to pull rows for values b or c if specified.

As always, you must test to determine the value of stats or indexes.


Dave

David W. Roth
Teradata Certified Master
TERADATA



     
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