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Message Posted: Wed, 01 Mar 2006 @ 12:21:47 GMT

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Subj:   Re: NUSI bitmapping
From:   ravivijay.kumar


This is basically used when a weakly selective index is use

Bit mapping is significantly faster than the three-part process of copying, sorting, and comparing rowID lists. Additionally, the technique dramatically reduces the number of base table I/Os required to retrieve the requested rows.

Teradata only performs NUSI bit mapping when weakly selective indexed conditions are ANDed. When WHERE conditions are connected by a logical OR, the Optimizer typically performs a full-table scan and applies the Ored conditions to every row without considering an index.


Vijay kumar.R

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