How to create primary on a column when redundant data is present

Question

I am interested to add primary key constraint on a column where repeated data is there without affecting the date how can I immplement this.
Can any one help me in this regard.
Thanks
Sanjay

Answer 1

If you have duplicated data and going to specify the primary key constraint on that data it's quite against RDBMS concepts and can't be considered as a relevant idea. Nevertheless Oracle provides you with such tricky method, but once again, it's NOT good idea, change your mind:
SQL> create table t (x int);
Table created.
SQL> insert into t values(1);
1 row created.
SQL> insert into t values(1);
1 row created.
SQL> commit;
Commit complete.
SQL> select * from t;
         X
         1
         1
SQL> create index t_x on t(x);
Index created.
SQL> alter table t add primary key (x) novalidate;
Table altered.
SQL> insert into t values(1);
insert into t values(1)
ERROR at line 1:
ORA-00001: unique constraint (ORACLE_OCM.SYS_C006647) violated
SQL> insert into t values(2);
1 row created.
SQL> select * from t;
         X
         1
         1
         2In this case you have PK constraint and it affects all new DMLs, but
in fact you can't rely on PK.
Rgds.