Mysql触发器

基于school数据库中的student, course, sc表,创建满足下述要求的触发器:

数据库navicat   cmd界面运行

1.对SC表进行插入或修改时,如果考试成绩不在0-100范围内时,则撤销插入或修改操作。

DELIMITER ;

DROP TRIGGER IF EXISTS `tri_update_grade`;

DELIMITER ;;

CREATE TRIGGER `tri_update_grade` BEFORE UPDATE ON `sc` FOR EACH ROW begin

if new.grade > 100 then

delete from sc;

elseif new.grade < 0 then

delete from sc;

end if;

end

;;

 

DELIMITER ;

DROP TRIGGER IF EXISTS `tri_insert_grade`;

DELIMITER ;;

CREATE TRIGGER `tri_insert_grade` BEFORE INSERT ON `sc` FOR EACH ROW begin

if new.grade > 100 then

delete from sc;

elseif new.grade < 0 then

delete from sc;

end if;

end

;;

 

2.对SC表进行插入时,如果学生的选课总学分超过30,则报错并撤销插入。

DELIMITER ;

DROP TRIGGER IF EXISTS `tri_insert_credit`;

DELIMITER ;;

CREATE TRIGGER `tri_insert_credit` BEFORE INSERT ON `sc` FOR EACH ROW begin

SELECT sum(Ccredit) INTO @sumcred from Student join SC on SC.Sno=Student.Sno join Course on Course.Cno=SC.Cno WHERE sc.Sno=new.Sno;

if (@sumcred>30)

then

delete from sc;

end if;

end

;;

 

 

 

 

 

 

3.对SC表进行修改时,不允许修改考试成绩不及格的学生选课记录。

DELIMITER ;

DROP TRIGGER IF EXISTS `tri_grade`;

DELIMITER ;;

CREATE TRIGGER `tri_grade` BEFORE UPDATE ON `sc` FOR EACH ROW begin

select grade INTO @gra from sc where sno=new.sno and sno=new.sno;

if (@gra >= 60)

then

set new.grade=20;

else

delete from sc;

end if;

end

;;

 

4.对STUDENT表进行插入时,如果年龄为空,则将该生年龄设置为所有学生年龄的平均值。

DELIMITER ;

DROP TRIGGER IF EXISTS `tri_student`;

DELIMITER ;;

CREATE TRIGGER `tri_student` BEFORE INSERT ON `student` FOR EACH ROW begin

select avg(Sage) INTO @avgage from student;

SET @old_age = new.Sage;

if @old_age IS NULL

then

set new.Sage=@avgage;

end if;

end

;;

 

 

5.在STUDENT表中增加两列,分别用来存放学生的平均成绩和等级,并对SC表进行插入后,自动维护学生的平均成绩和等级(85-100,等级为“优"; 60-85,等级为“良”,60 以下,等级为“差")

DELIMITER ;

DROP TRIGGER IF EXISTS `tri_comment`;

DELIMITER ;;

CREATE TRIGGER `tri_comment` BEFORE UPDATE ON `student` FOR EACH ROW begin

select avg(Grade) INTO @avggra from sc where sno=new.sno;

if @avggra > 85 then

update sc set new.Savg=@avggra,new.Scomment="you";

else if @avggra > 60 and @avggra <= 85 then

update sc set new.Savg=@avggra,new.Scomment="you";

else

update sc set new.Savg=@avggra,new.Scomment='cha';

end if;

end if;

end

;;

DELIMITER ;

 

数据库链接:https://pan.baidu.com/s/1_OtHuZHF86HRMVY9ROn3xQ    提取码:kr9l

上一篇:7473-42-9,Methyl 2,3,5-tri-O-Benzoyl-α-D-arabinofuranoside,甲基 2,3,5-三-O-苯甲酰基-α-D-呋喃阿拉伯糖苷


下一篇:利用生成器输出杨辉三角