在数据库中记录员工和员工工作信息,要求当某个员工离职后,数据库自动删除该员工的工作信息。则在定义工作信息表时,对于外关键字的删除规则应定义为

A.ON DELETE ROLLBACK

B.ON DELETE CASCADE

C.ON DELETE SET NULL

D.ON DELETE NO ACTION

A.INSTEAD OF DELETE

B.INSTEAD OF DROP

C.AFTER DELETE

D.AFTER UPDATE

A.INSTEAD OF DELETE

B.INSTEAD OF DROP

C.AFTER DELETE

D.AFTER UPDATE

A.从员工数据库中检索销售部的平均工资 

B.从员工数据库中检索销售部和其他部门的平均工资

C.从员工数据库中检索销售部和其他部门的总工资

D.从员工数据库中检索除了销售部以外其他部门的平均工资

A.INSTEAD OF DELETE

B.INSTEAD OF DROP

C.AFTER DELETE

D.AFTER UPDATE

A.INSTEAD OF DELETE

B.INSTEAD OF DROP

C.AFTER DELETE

D.AFTER UPDATE