Re: Selectivity

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.

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