You can enforce referential integrity with unenforced foreign keys.
DEPT table { DeptNo int primary key DeptName varchar(20), Mgr int, foreign key MGR_EMPNO (Mgr) references EMPLOYEE(EmpNo) on update restrict } EMPLOYEE table { EmpNo int primary key, DeptNo int references DEPT(DeptNo) on delete restrict, LastName varchar(20), FirstName varchar(20), Salary int }