Helen, I think you are wrong here. I have a table with about 100.000
records and index on on column which can have only 3 diferent values.
Selectivity for thet index show value 0.333, which means that it is computed
as (1/count of unique values).

regards
Zile

-----Original Message-----
From: Helen Borrie [mailto:helebor@...]
Sent: Sunday, August 19, 2001 14:37
To: ib-support@yahoogroups.com
Subject: Re: [ib-support] Index on Boolean-Col


At 01:25 PM 19-08-01 +0200, you wrote:

>Just for me to remember, selectivity is (1 / count of unique values) ?
>And what does selectivity exactly mean and what it is used for ?

AFAIK, it is the count of unique values / count of values.