（1）在两个表间建立为维护参照完整性使用的级联删除触发器、级联修改触发器和受限插入触发器。 （2）建立一个学生选课数不超5门的触发器； （3）建立一个触发器，教授工资不得低于4000元，若低于4000，自动改为4000元。 （4）建立一个触发器，当对表SC的grade属性修改时，若分数增加了10%，则将此次操作记录到另一个表SC_U(sno,cno,Oldgrade,Newgrade)中，其中Oldgrade修改前的分数,Newgrade修改后的分数。

（1）建立级联删除触发器：

CREATE TRIGGER tr_del_course
ON course
FOR DELETE
AS
BEGIN
    DELETE FROM score WHERE cno IN (SELECT cno FROM deleted)
END

CREATE TRIGGER tr_del_student
ON student
FOR DELETE
AS
BEGIN
    DELETE FROM score WHERE sno IN (SELECT sno FROM deleted)
END

建立级联修改触发器：

CREATE TRIGGER tr_update_course
ON course
FOR UPDATE
AS
BEGIN
    UPDATE score SET cno = inserted.cno WHERE cno IN (SELECT cno FROM deleted)
END

CREATE TRIGGER tr_update_student
ON student
FOR UPDATE
AS
BEGIN
    UPDATE score SET sno = inserted.sno WHERE sno IN (SELECT sno FROM deleted)
END

建立受限插入触发器：

CREATE TRIGGER tr_insert_score
ON score
FOR INSERT
AS
BEGIN
    IF (SELECT COUNT(*) FROM score WHERE sno = inserted.sno) >= 5
        RAISERROR ('每个学生最多只能选5门课程！', 16, 1)
END

（2）建立学生选课数不超过5门的触发器：

CREATE TRIGGER tr_insert_score
ON score
FOR INSERT
AS
BEGIN
    DECLARE @sno CHAR(10)
    SET @sno = (SELECT sno FROM inserted)
    IF (SELECT COUNT(*) FROM score WHERE sno = @sno) >= 5
    BEGIN
        RAISERROR ('每个学生最多只能选5门课程！', 16, 1)
        ROLLBACK TRANSACTION
    END
END

（3）建立教授工资不得低于4000元的触发器：

CREATE TRIGGER tr_update_teacher
ON teacher
FOR UPDATE
AS
BEGIN
    IF EXISTS (SELECT * FROM inserted WHERE salary < 4000)
    BEGIN
        UPDATE teacher SET salary = 4000 WHERE tid IN (SELECT tid FROM inserted WHERE salary < 4000)
    END
END

（4）建立当对表SC的grade属性修改时，若分数增加了10%，则将此次操作记录到另一个表SC_U(sno,cno,Oldgrade,Newgrade)中的触发器：

CREATE TRIGGER tr_update_score
ON score
FOR UPDATE
AS
BEGIN
    DECLARE @sno CHAR(10), @cno CHAR(10), @Oldgrade DECIMAL(5,2), @Newgrade DECIMAL(5,2)
    SELECT @sno = sno, @cno = cno, @Oldgrade = deleted.grade, @Newgrade = inserted.grade 
    FROM inserted INNER JOIN deleted ON inserted.sno = deleted.sno AND inserted.cno = deleted.cno
    IF @Newgrade > @Oldgrade * 1.1
    BEGIN
        INSERT INTO SC_U (sno, cno, Oldgrade, Newgrade) VALUES (@sno, @cno, @Oldgrade, @Newgrade)
    END
END