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Message Posted: Wed, 09 Mar 2005 @ 21:41:16 GMT


     
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Subj:   Re: Use of Indexes in Teradata
 
From:   GORRELLA, SRINI (SBCSI)

Srikanth,

It all depends on the cardinality .. NUSIs are equally good and bad . It all depends on percent of rows per NUSI values . If you have more rows that qualify NUSI value then you will end up reading almost each and every data block , the no: of I/O operations undertaken by the retrieval could easily exceed the number required for a FTS (full table scan).. So in these cases table scans are much more efficient then NUSI access

So we cannot just go with a thumb rule that NUSIs are always good . You need to closely look into data demographics for NUSI creation

Hope this helps


Thanks,

Srini



     
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