Creating an unique index instaed of using primary key index

Question

Hi ,
I heard in a debate sometimes it's better to create a unique index on a column and using it instaed of using primary key index in oracle.I couldn't understand what the reason propely.
Can anyone please help me in thsi topic if it is a valid one .
Thanks in advance

Answer 1

Hi,
They are exactly NOT identical.
1. Unique key can have NULL values where primary keys can't.
2. Primary key is fundamentally those keys which do not change. I mean updating a primary key is not a good idea.
SQL> drop table test;
Table dropped.
SQL> create table test ( a number(2));
Table created.
SQL> ed
Wrote file afiedt.buf
  1* create unique index test_idx on test(a)
SQL> /
Index created.
SQL> ed
Wrote file afiedt.buf
  1* insert into test values(NULL)
SQL> /
1 row created.
SQL> drop table test;
Table dropped.
SQL>
SQL> create table test ( a number(2) primary key);
Table created.
SQL> insert into test values(NULL);
insert into test values(NULL)
ERROR at line 1:
ORA-01400: cannot insert NULL into ("HR"."TEST"."A")
SQL>Cheers,
Edited by: Avinash Tripathi on Nov 24, 2009 11:17 AM