Re: Creating Table as select...

KDB wrote:

> Hi Daniel,
> I read the following in oracle 10g concepts manual:
>
> http://download-west.oracle.com/docs/cd/B12037_01/server.101/b10743/schema.htm#sthref893
>
> <Oracle10gConcepts>
>
> Unique and Nonunique Indexes
> Indexes can be unique or nonunique. Unique indexes guarantee that no
> two rows of a table have duplicate values in the key column (or
> columns). Nonunique indexes do not impose this restriction on the
> column values.
>
> Oracle recommends that unique indexes be created explicitly, and not
> through enabling a unique constraint on a table.
>
> </Oracle10gConcepts>
>
> Can you please comment on this!
>
> --KDB
Don't mind at all Howard. But my answer will be a bit less kind.

Whoever wrote that has little or no experience in the real-world. They are an Oracle employee creating documentation and likely have never had the experience of creating or managing applications in the real-world.

If you are going to create a unique index by all means follow the above advice. A better question is why create one at all? You gain nothing. You lose a lot.

BTW: The question of unique index vs. unique constraint is one I routinely ask during job interviews. Those that don't know the difference don't get hired.

-- 
Daniel Morgan
http://www.outreach.washington.edu/ext/certificates/oad/oad_crs.asp
http://www.outreach.washington.edu/ext/certificates/aoa/aoa_crs.asp
damorgan_at_x.washington.edu
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