Re: nonunique index on unique values


"ciapecki" <ciapecki@xxxxxxxxx> wrote in message
news:1188285737.311072.16590@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
hi,

is there a big lost in performance if there is a nonunique index on
the column that holds only unique values (like primary key)?

thanks
chris



The index content will be one byte per row larger,
and there are a few cases where the arithmetic the
optimizer uses changes if you switch a unique index
to non-unique.

Neither is necessarily a problem - but you can always
find a few unlucky cases where performance changes
dramatically because an execution plan has changed.

--
Regards

Jonathan Lewis
http://jonathanlewis.wordpress.com

Author: Cost Based Oracle: Fundamentals
http://www.jlcomp.demon.co.uk/cbo_book/ind_book.html

The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html


.

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