Re: using index

From: Karen Paulsell <karenp_at_sybase.com>
Date: 1998/10/11
Message-ID: <6vouuk$sbf@fyi.sybase.com>#1/1

If you're aksing about Sybase, it will use an index for is null queries but not (in the test I just tried) for 'is not null'.

The exception being covered queries: if you have a covering index, is not null queries will use it.

In article <361fa67c.3119854_at_news.siol.net> jmodic_at_src.si (Jurij Modic) writes:
>On 10 Oct 1998 03:53:51 GMT, paulkcng_at_news.netvigator.com (Ng K C
>Paul) wrote:
>
>>What about ' is null ' and ' is not null '? Will it have the same behaviour
>>as ' =" " ' and ' <>" " ' ?
>
>No, ordinary B-tree indexes do not store null values, so "is (not)
>null" condition will never use indexes. Bitmap indexes are different,
>they store bitmaps also for null values, so "is null" predicates can
>use bitmap indexes.
>
>HTH,
>--
>Jurij Modic <jmodic_at_src.si>
>Certified Oracle7 DBA (OCP)
>================================================
>The above opinions are mine and do not represent
>any official standpoints of my employer
Received on Sun Oct 11 1998 - 00:00:00 CDT