Create a primary key auto-increment table in Oracle

-- Create a table and Set primary key auto-Increment
Create Table Stu (
Uerid number (4) not null primary key,
Username varchar (20 ),
Userpass varchar (20 ),
Email varchar2 (30 ),
Grade number (5)
);
Commit;
-- Check it.
Select * from Stu;
-- Create an auto-incrementing sequence of the primary key
Create sequence emp_sequence
Increment by 1
Start with 1
Nomaxvalue
Nocycle
Nocache;
Commit;
-- Create a trigger
Create trigger "trigger_on_stu" before
Insert on Stu for each row when (New. uerid is null)
Begin
Select emp_sequence.nextval into: New. uerid from dual;
End;
-- Insert data
Insert into Stu (username, userpass, email, grade) values ('admin', 'admin', 'admin @ admin.com ', 1 );
Insert into Stu (username, userpass, email, grade) values ('dhy', 'dhy', 'dhy @ admin.com ', 1 );
Insert into Stu (username, userpass, email, grade) values ('ns', 'ns', 'ns' @ admin.com ', 1 );
Insert into Stu (username, userpass, email, grade) values ('adamin', 'addmin', 'admdin @ admin.com ', 5 );
Insert into Stu (username, userpass, email, grade) values ('dhay', 'dhay', 'dhay @ admin.com ', 3 );
Insert into Stu (username, userpass, email, grade) values ('ansr', 'ansr', 'ansr @ admin.com ', 4 );
Commit;
-- View data
Select * from Stu;