Re: using index

What is covering index?

Karen Paulsell (karenp_at_sybase.com) wrote:
: 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 Mon Oct 12 1998 - 00:00:00 CDT