How we can create a trigger in which changes on emp salary or pf his total salary change.

If I understand the question correctly you need to add base, pf, and da to calculate total in case any of those change.

If this is the case then the trigger could look something like

CREATE TRIGGER employee_trigger
ON employee
AFTER INSERT, UPDATE AS
BEGIN
   UPDATE e
   SET e.emp_total = COALESCE(e.emp_base, 0)
                     + COALESCE(e.emp_Pf, 0)
                     + COALESCE(e.emp_DA, 0)
   FROM employee e INNER JOIN inserted i
   ON e.emp_id = i.emp_id;
END;

There are two things to notice, first I've used a join since a single SQL statement may change several rows in a table and in such case this trigger would be run only once. In that situation the inserted table would contain one row for each row changed.

The other thing is the use of COALESCE. Based on your table definition, any of the three columns may be NULL so in such case I replaced the NULL with zero.


However, I wouldn't actually solve the problem this way. Much easier way would be to use computed columns. This would also yield to much better performance.

So if the total is calculated based on those columns I would simply define the table as follows

CREATE TABLE employee(
   emp_id    int,
   emp_name  varchar(50),
   emp_base  money,
   emp_Pf    money,
   emp_DA    money,
   emp_total AS COALESCE(emp_base, 0) 
                + COALESCE(emp_Pf, 0) 
			    + COALESCE(emp_DA, 0)
);