--       --
Create Table Emp
(
  Emp_ID        Number(10),
  Emp_Code      VarChar2(10),
  Emp_Name      VarChar2(50),
  Constraint PK_EMP Primary Key(Emp_ID)
)
/

Create Or Replace Trigger TRG_EMP Before Insert Or Update Or Delete On Emp
For Each Row
Declare
  ID_Serial       Number(10);
Begin
  If(Inserting)Then
     Select NVL(Max(Emp_ID),0) Into ID_Serial From Emp;
     
     ID_Serial := ID_Serial + 1;
     
     :New.Emp_ID := ID_Serial;
     
     
     --   --
     -- Select NVL(Max(Emp_ID),0) + 1 Into :New.Emp_ID From Emp;
  End If;
End;
/
