MySQL setting trigger problem

The enterprise database given under the examinee folder db_ emp Including employees surface tb_ employee And department Door Watch tb_ dept.

The employee table has a department number (deptno) , Wages (salary) , The Department table has department ] Number (deptno) 、 Department name (dname)

Design a project named t_ emp The trigger of , The completed function is : When the delete Records in the Department table , Put the department number in the employee table (deptno) Set up empty . And use the command to delete the department number (deptno) by D2 The row of triggers this trigger , And look at the results .