RE: Primary Constraints and Indexes

From: Sachin Puri <sachin_at_siworldwide.com>
Date: Thu, 11 Jan 2001 13:26:43 +0530
Message-Id: <10737.126378@fatcity.com>

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-----
From: Wayne McGill [mailto:McGillWL_at_navair.navy.mil] Sent: Wednesday, January 10, 2001 9:16 PM To: Multiple recipients of list ORACLE-L Subject: Primary Constraints and Indexes

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

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Author: Wayne McGill
  INET: McGillWL_at_navair.navy.mil

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