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Message Posted: Thu, 31 May 2012 @ 13:45:34 GMT


     
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Subj:   Multi-column statistics and truncation
 
From:   Gregg, William

I was on the Developer Exchange and took a moment to read some of Carrie B's recent stuff and found this gem that is available in v14:

The new default limit for the size of the histogram values fields is 25 bytes in Teradata 14.0. However, the limit can be increased by specifying a greater value on the COLLECT STATISTICS statement itself. The ordering of the multicolumn statistics can now be specified on the COLLECT STATISTICS statement as well (with the exception of statements that specify INDEX).

In addition, each participating column in a multicolumn stat will be represented by at least 25 bytes (if it needs it), and truncation will only take place after the column's leading 25 bytes have been represented, on a column by column basis.

Prior to the 14.0, not only was the truncation at 16 bytes, but it was the first 16 bytes in the combined values strung together. If you had several different columns in the statistic, often the later ones would not be represented at all. That will no longer be the case.

Thanks, -Carrie


It is great to see that Teradata is directly addressing the limitations that the leading, 16 byte truncation rule has imposed on multi- column stats.

Rgrds,

Bill Gregg
Teradata DBA; Data Warehousing, BI Team



     
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