Posted by Alexander Kuznetsov on 06/09/06 21:09

>
> select * from tblnames where firstname = 'john'--Performed a Table Scan
>

If you only select 2 columns, firstname, lastname

select columns, firstname from tblnames where firstname = 'john'

and the table has a lot of other columns, the index is likely to be
used even if firstname is not the first column in the index. The reason
is simple: the index contains all the information necessary to satisfy
the query and it is smaller than the table.

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