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Posted by jim_geissman on 10/20/06 10:02
How can this be true? In this case, the computed column is simply
a substring of one of the other columns that is already in the query,
and is also included in the 3-item index. Is this really too hard for
the
optimizer?
> I don't believe the optimiser can break down a computed column to know
> which underlying columns it is based upon. So it doesn't know that the
> computed column is "covered" by a particular index. Of course, you can
> index computed columns, and it might then use that index, if it was a
> covering index.
>
> Damien
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