indexes and keys

Greetings - I hope this is a simple question.

Is there any reason to create an index on a column that already has one
created as part of a SERIAL datatype?  That is, I used:

CREATE TABLE personal_data (id serial ...);

to create it, so \d shows:
| postgres         | personal_data                    | table    || postgres         | personal_data
|table    || postgres         | personal_data_id_key             | index    || postgres         | personal_data_id_seq
          | sequence |
 

is there any reason to create another index on id:

CREATE INDEX pd_id_idx on personal_data;

or will the automatically created one be sufficient?

Thanks.

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Andrew J. Perrin - aperrin@demog.berkeley.edu - NT/Unix Admin/Support
Department of Demography    -    University of California at Berkeley
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http://demog.berkeley.edu/~aperrin --------------------------SEIU1199