Unique Constraints in Oracle

Unique Key

• Its a entity and integrity.
• It ignores duplicates.
• It accept null values and multiple null values.
• Its automatically generates unique as index.

Scenario : 

consider one table name as course234 and column are course table is  CId and CName. Here set cid is unique key.

Syntax : 

create table course( CId Number, CName varchar(2) constraints c2 unique(CId)) ;

Table Created;

insert into course234 values(1,'parthi');
insert into course234 values(2,'karthi');

Two Rows Inserted

insert into course234 values(1,'prakash');

when inserting this third row face this error 

ORA-00001: unique constraint (HR.C1) violated 

insert into course234 values(null ,'prakash');

1 row inserted

Note: Here Cid value is 1 Its already inserted. The main thing in the unique constraints is ignores duplicate values but it accept null values.

select * from course234;

Output :

CID CNAME
1 parthi
2 karthi
- prakash