Re: NULL Values in Indexes - Confused

A copy of this was sent to Dipen Kotecha <dkotecha_at_ford.invalid> (if that email address didn't require changing) On Thu, 12 Aug 1999 15:01:20 +0200, you wrote:

>We have a table with 1.2 million records which is regularly queried to
>see whether a date field is NULL. I understand that NULL values are not
>stored in indexes, so if I created an index on this date field, would it
>be used in the query? Approx. 10% of the data contains a NULL date
>field.
>
>Dipen

A query such as:

select * from T where X is null;

will never use an index. The rows where X is null would not be stored in an index on X.

A full scan would result.

--
See http://govt.us.oracle.com/~tkyte/ for my columns 'Digging-in to Oracle8i'... Current article is "Part I of V, Autonomous Transactions" updated June 21'st  

Thomas Kyte                   tkyte_at_us.oracle.com
Oracle Service Industries     Reston, VA   USA

Opinions are mine and do not necessarily reflect those of Oracle Corporation Received on Thu Aug 12 1999 - 08:41:36 CDT