Primary Key in Oracle

Primary Key

• It is a entity integrity.
• It ignore Null values.
• It ignore duplicates.
• only one primary key accepted in a table.
• It automatically create unique index.

Primary Key = Unique Key + Not Null

Scenario : 

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

Syntax : 

create table course123( CId Number, CName varchar(2) constraints c1 primary key(CId)) ;

Table Created;

insert into course123 values(1,'parthi');
insert into course123 values(2,'karthi');

Two Rows Inserted

insert into course123 values(1,'prakash');

when inserting this third row face this error 

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

Note: Here Cid value is 1 Its already inserted). The main thing in the primary key constraints is ignores null values and duplicates.