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Message Posted: Wed, 05 Aug 2015 @ 12:06:16 GMT


     
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Subj:   Re: NoPI tables as Staging tables
 
From:   Dave Wellman

Hi,

Yes, I think that is a reasonable conclusion.

Sure, some types of conditions are less likely to use a NUSI (inequality being one of them).

I ran a small test (TD 15.0.1) with a simple table:

     CREATE TABLE t1
     (col1 INTEGER NOT NULL
     ,col2 INTEGER NOT NULL
     ,col3 CHAR(200)
     )
     UNIQUE PRIMARY INDEX ( col1 )
     INDEX ( col2 );

I loaded 159K rows into the table and set the values of COL2 so that

- 3 rows had a value = 2

- all other rows had a value = 1


I collect statistics on COL1 and COL2 (as separate columns).

Explaining each of the following queries gives:

     SELECT *
     FROM t1
     WHERE col2 = 2;
     - uses the NUSI

     SELECT *
     FROM t1
     WHERE col2 = 1;
     - does a FTS

     SELECT *
     FROM t1
     WHERE col2 <> 1;
     - uses a NUSI

Yes this is a simple test case using contrived data, but I think it demonstrates the point.


Cheers,

Dave

Ward Analytics Ltd - Information in motion (www.ward-analytics.com)



     
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