2007/5/23, Becker, Holger <[EMAIL PROTECTED]>:
Daniel Castro wrote:
> Hi,
>
> I have some queries doing a SCAN. I identify then and I
> create a index.
>
> For example:
>
> explain SELECT PSV.PSV_COD , PSV.PSV_APEL ,
> PSV.PSV_TRAT , PSV.PSV_TIPO FROM PSV WHERE (
> PSV.PSV_TIPO<> 'I' ) ORDER BY
> PSV.PSV_APEL ASC
>
> Results:
> DBA PSV TABLE SCAN 1019
> DBA RESULT IS NOT COPIED , COSTVALUE IS 1019
>
> I created a index on PSV.PSV_TIPO <> 'I' but the query is
> scanning the
> table again.
> After the index xreatino I have to do some other thing?
>
> Best regards,
Hi,
there is nothing to do after index creation.
The index would be used if the optimizer would estimate less I/O costs
for the possible index strategy.
In your case the scan seems to be less expensive than the index access.
This would be the case if the condition PSV.PSV_TIPO <> 'I' is not
very selective.
Which is usually the case for *exclusions*. Also, that an index seek
can usually be done only for equality (i.e. col = 1) - for all others
typically scans of part or the whole index occur.
Kind regards
robert
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