Re: Selectivity
Date: Wed, 30 Apr 2003 10:33:07 +0000
Message-ID: <2824007.1051698787_at_dbforums.com>
Originally posted by Gorang
> Could someone, please, shed some light on why for selectivity (s)
> defined as the ratio of the number of tuples that satisfy the
> condition to the total number of tuples in the relation, and hence a
> number between 0 and 1, it is often (allways?) said that high
> selectivity corresponds to low value of this ratio and low selectivity
> corresponds to the high value of such ratio ?!
>
> ( GoranG79 AT hotmail.com )
A query has "highly selectivity" if it returns a small proportion of the
rows, and "low selectivity" if it returns a large proportion of the
rows. There is no contradiction.
Analogy: it's like saying I'm a HIGHLY fussy eater because I will only eat a SMALL proportion of the types of food available, but you are LESS fussy because you will eat a LARGE proportion.
-- Posted via http://dbforums.comReceived on Wed Apr 30 2003 - 12:33:07 CEST