Vishak,
Unique constraints by default leads to creation of a
unique index by Oracle. This index is used for
imposing uniqueness. If you have a unique index in
mind then constraint is the way to go.
- An explicit constraint allows you to use Oracle
mechanisms to trap exceptions in another table while
ENABLEing a previously disabled constraint or trap
errors in your code.
- Optimizer can make use of constraint declarations
for query rewrite.
- If you are 8i you can define a unique constraint in
DISABLEd VALIDATE mode and have Oracle skip the
automatic creation of Index. If you are a
datawarehouse environment you can still have the
optimizer make use of the constraint for query rewite
even if the index is not there.
- Constraint declaration gives you lots of
flexibility on when to kick in the check. For OLTP
environment you can defer constraint checks depending
on your transaction's needs (in 8i).
There is gobs of information in the SQL ref manual on
syntax and the options I have mentioned above.
HTH
- Sundeep
PS: I used to work for Wipro in 1987. I am wondering
if the likes of Ashok Soota and Manoj Chug are still
part of the company. You can send me email at my
personal email address.
Thanks
- Vishak <vishak.holla_at_wipro.com> wrote:
> Hello Gurus,
>
> I would like to know whether creating an
> unique-index on a column or a
> unique constraint on a column(during creation of the
> table) would be fine.
>
> Which option would be better?
>
> TIA
> Regards
> Vishak
>
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.com
> --
> Author: Vishak
> INET: vishak.holla_at_wipro.com
>
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Sundeep Maini
Consultant
Currently on Assignement at Marshfield Clinic WI
mainis_at_mfldclin.edu
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--
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--
Author: sundeep maini
INET: sundeep_maini_at_yahoo.com
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San Diego, California -- Public Internet access / Mailing Lists
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Received on Fri Jun 01 2001 - 11:18:24 CDT
