The major difference between a primary key and an
unique index is if you want to enforce referential
integrity you need a primary key to do so.
James
--- Sachin Puri <sachin_at_siworldwide.com> wrote:
>
> A Primary Key is a unique identification of a row in
> a database table.
> When a primary key is created an index is also
> created implicitly on that
> column.So u don't
> need any explicit index on that column which has a
> primary key constraint.
> There can be only one Primary Key in a table however
> u can have a number of
> indexes in a table.(depends on the oracle release as
> in Oracle 7.x u can
> have 16 indexes in a table)
> Explicit Indexes are generally used for fast data
> retrieval and perfomance
> enhancement.
>
>
> Rgds,
> Sachin Puri
> Oracle Development and Administration
> Solutions Infosystems
>
>
> -----Original Message-----
> Sent: Wednesday, January 10, 2001 9:16 PM
> To: Multiple recipients of list ORACLE-L
>
>
> As a part-time dba, I am confused about the
> differences between
> Primary Keys and Indexes.
>
> For example if I create a table "EMPLOYEES" and in
> the table
> creation statement I do something like:
> create table ...
> constraint XXX primary key (EMP_ID) using
> index ...
> then later I create an index:
> create index YYY on EMPLOYEE (EMP_ID) ...
> I know I have created two indexes (the first one
> system-named
> and implicitly created and the second name YYY and
> created
> explicitly) but do I really need the second index
> YYY?
> It seems to me the YYY index is not really needed?
> Can
> someone shed some light on this for me.
>
> THANKS, Wayne
> McGillWL_at_navair.navy.mil
>
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.com
> --
> Author: Wayne McGill
> INET: McGillWL_at_navair.navy.mil
>
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> --
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>
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Received on Fri Jan 12 2001 - 16:29:07 CST
