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Home -> Community -> Usenet -> c.d.o.server -> Re: using index
All the columns that you asked for are included in the index.
Ie, table with column a,b,c,d
index on a,b,c
If you select a,b from table, all the data you asked for is in the index, so we don't have to scan the data level.
See "Covered Queries" in the ASE 11.5 Performance and Tuning Guide.
Ng K C Paul wrote:
>
> 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.
> :
-- Bret Halford Imagine my disappointment Sybase Technical Support in learning the true nature 3665 Discovery Drive of rec.humor.oracle... Boulder, CO 80303Received on Sun Oct 11 1998 - 00:00:00 CDT
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