Hi,

> Excuse me Ivan...
>
> Selectivity is
> SingleRowInTable / TotalRows
>
> In PK this is 1 and index has the better selectivity
>
> when SingleRowInTable become < TotalRows then selectivity decrease --> 0
> so bigger values (near 1) are better for selectivity.
>
> I'm wrong?

Yes you're wrong ;-)
Ivan is completly right the lower the selectivity the beter.

Calculated selectivity is with this formula :

Selectivity = 1.0 / (Nr_of_index-entries - Nr_of_duplicates)

If the number of duplicates is high in the index then the index-selectivity
value is higher, but worser to use.

Regards,
Arno Brinkman
ABVisie

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