Using triggers for referential integrity - sql-server

Question

There are 2 tables in the database that contain the following columns:
department table with column dept_no (char(4), not null)
employee table with column dept_no (char(4), null)
The dept_no column needs to be defined as a primary key in the department table and a foreign key in the employee table using a trigger.
I thought this was the correct solution using the deleted and inserted virtual tables to update/delete the foreign key in the corresponding employee table:
CREATE TRIGGER trig_delete_dept_no
ON department
AFTER DELETE
AS
UPDATE employee
SET employee.dept_no = NULL
FROM deleted
WHERE employee.dept_no = deleted.dept_no
CREATE TRIGGER trig_update_dept_no
ON department
AFTER UPDATE
AS
UPDATE e
SET e.dept_no = i.dept_no
FROM employee e
INNER JOIN inserted i ON e.dept_no = i.dept_no
However, when I update the department dept_no row to a different value I do not see the corresponding dept_no update in the employee table:
UPDATE department
SET dept_no = 'd4'
WHERE dept_no = 'd3'
Deleting functions as expected. What am I doing wrong with the update trigger and how can I combine these two triggers into one trigger?

Answer 1

There is an issue in your design. The first thing is you should not use dept_no as PK (Primary Key). You need to have an IDENTITY or GUID column as Primary Key and refer to that column as FK (Foreign Key).
This way you won't need to worry about changing the dept_no.
The second point is you don't need trigger. you can use CASCADE option on DELETE action.
Find more information on CASCADE

Answer 2

Thank you FLICKER and SMor for helping me think through this. I do not believe the assignment wants us to modify the tables by adding IDENTITY or GUID columns and since we are to strictly use Triggers, this is the best solution I can come up with:
CREATE TRIGGER trig_delete_dept_no ON department AFTER DELETE AS
UPDATE employee
SET employee.dept_no = NULL
FROM deleted
WHERE employee.dept_no = deleted.dept_no
CREATE TRIGGER trig_update_dept_no ON department AFTER UPDATE AS
IF UPDATE(dept_no)
BEGIN
IF (SELECT employee.dept_no
FROM employee, inserted
WHERE employee.dept_no = inserted.dept_no) IS NULL
BEGIN
ROLLBACK TRANSACTION
RAISERROR ('Integrity constraint violation, TRIGGER:
trig_update_dept_no, TABLE: department',16,1)
END
ELSE PRINT 'Update successful'
END
This will allow updates to occur in the department as long as there are no orphaned records in the employee table.