实验六、完整性控制（包含触发器的使用方法）——SQLServer触发器

一、实验目的

1．掌握数据库完整性控制原理
2．掌握SQL Server数据库系统完整性控制方法

二、实验内容

1． 创建一个触发器，“数据库”课程的选课人数不能超过5人。
2．.创建一个触发器，规定每位同学选课门数不能超过3门。
3． 创建一个触发器，当修改成绩表中成绩时，如果变化幅度超过10%，将操作记录在下表SC_U（Sno,Cno,Oldgrade,Newgrade）中。

三、过程以及记录

1．写出你操作并正确执行的代码及结果。

1、创建一个触发器，“数据库”课程的选课人数不能超过5人。

创建一个触发器，“数据库”课程的选课人数不能超过5人。

--创建触发器
CREATE TRIGGER myFristNotByCount ON T.SC
AFTER INSERT,UPDATE
AS 
DECLARE @Count INT,@Cno CHAR(4),@Sno CHAR(9)
SELECT @Count = COUNT(*) FROM T.Course a,T.SC b
WHERE a.Cno = b.Cno AND a.Cname = '数据库';

SELECT @Sno = Sno,@Cno = Cno FROM INSERTED;
IF(@Count>5)
BEGIN
DELETE FROM T.SC WHERE Sno = @Sno AND Cno = @Cno;
END

--测试
INSERT INTO T.SC VALUES('201215121',1,52),
('201215122',1,52),('201215123',1,52),
('201215125',1,52),('201215126',1,52),('201215127',1,52);

--查询数据库的选课记录
SELECT  COUNT(*) 数量 FROM T.Course a,T.SC b
WHERE a.Cno = b.Cno AND a.Cname = '数据库';

2、创建一个触发器，规定每位同学选课门数不能超过3门。

创建一个触发器，规定每位同学选课门数不能超过3门。

--创建触发器
CREATE TRIGGER MyTriggerByCourse ON T.SC
AFTER INSERT
AS
DECLARE @Count INT,@Sno CHAR(9),@Cno CHAR(4)
SELECT @Sno = Sno,@Cno = Cno FROM INSERTED;
SELECT @Count = COUNT(*) FROM T.SC;
IF(@Count>3)
BEGIN 
DELETE FROM T.SC WHERE Sno = @Sno AND Cno = @Cno;
END

--测试（两个人分别添加6条选课记录）
INSERT INTO T.SC VALUES('201215121',1,52),
('201215122',1,52),('201215123',1,52),
('201215125',1,52),('201215126',1,52),('201215127',1,52);

INSERT INTO T.SC VALUES('201215121',2,52),
('201215122',2,52),('201215123',2,52),
('201215125',2,52),('201215126',2,52),('201215127',2,52);

--验证
SELECT  a.Cno 课程名,a.Cname,COUNT(a.Cno) 数量 FROM T.Course a,T.SC b
WHERE a.Cno = b.Cno 
GROUP BY a.Cno,a.Cname;

3、创建一个触发器，当修改成绩表中成绩时，如果变化幅度超过10%，将操作记录在下表SC_U（Sno,Cno,Oldgrade,Newgrade）中。

创建一个触发器，当修改成绩表中成绩时，如果变化幅度超过10%，将操作记录在下表SC_U（Sno,Cno,Oldgrade,Newgrade）中。

--创建表T.SC_U
CREATE TABLE T.SC_U(
id INT IDENTITY(1,1),
Sno CHAR(9),
Cno CHAR(4),
Oldgrade SMALLINT,
Newgrade SMALLINT,
UpdateTime datetime,--更新时间
PRIMARY KEY(id),
FOREIGN KEY (Sno) REFERENCES T.Student(Sno),
FOREIGN KEY (Cno) REFERENCES T.Course(Cno)
)

--创建触发器
CREATE TRIGGER MyTriggerGradeUpdate ON T.SC
AFTER UPDATE
AS
DECLARE @Grade_old SMALLINT,@jexianZ SMALLINT,@jexianJ SMALLINT,@Grade_new SMALLINT,@Sno CHAR(9),@Cno CHAR(4)
SELECT @Grade_old = Grade,@Sno = Sno,@Cno = cno FROM DELETED;
SELECT @Grade_new = Grade,@Sno = Sno,@Cno = Cno FROM INSERTED;
SET @jexianZ = @Grade_old+@Grade_old*0.1;
SET @jexianJ = @Grade_old-@Grade_old*0.1;
IF(@Grade_new > @jexianZ)
BEGIN
PRINT('增幅的界限为：');
PRINT(@jexianZ);
INSERT INTO T.SC_U VALUES(@Sno,@Cno,@Grade_old,@Grade_new,GETDATE())
END
IF(@Grade_new < @jexianJ)
BEGIN
PRINT('向下增幅的界限为：');
PRINT(@jexianJ);
INSERT INTO T.SC_U VALUES(@Sno,@Cno,@Grade_old,@Grade_new,GETDATE())
END

结果截图：

——————————————————————————————————
测试触发器

--测试
--向上幅度大于10%
select * FROM T.SC WHERE Sno ='201215127' AND Cno = '1';--原始值
UPDATE T.SC SET  Grade = '90' WHERE Sno ='201215127' AND Cno = '1';
select * FROM T.SC WHERE Sno ='201215127' AND Cno = '1';--更新后的值
SELECT * FROM T.SC_U WHERE Sno ='201215127' AND Cno = '1';--查表检查结果是否被记录是否被记录

——————————————————————————————————

--向上幅度小于10%
select * FROM T.SC WHERE Sno ='201215127' AND Cno = '1';
UPDATE T.SC SET  Grade = '73' WHERE Sno ='201215127' AND Cno = '1';
select * FROM T.SC WHERE Sno ='201215127' AND Cno = '1';
SELECT * FROM T.SC_U WHERE Sno ='201215127' AND Cno = '1';

——————————————————————————————————

--向下幅度大于10%
select * FROM T.SC WHERE Sno ='201215126' AND Cno = '1';
UPDATE T.SC SET  Grade = '30' WHERE Sno ='201215126' AND Cno = '1';
select * FROM T.SC WHERE Sno ='201215126' AND Cno = '1';
SELECT * FROM T.SC_U WHERE Sno ='201215126' AND Cno = '1';

——————————————————————————————————

--向下幅度小于10%
select * FROM T.SC WHERE Sno ='201215126' AND Cno = '1';
UPDATE T.SC SET  Grade = '24' WHERE Sno ='201215126' AND Cno = '1';
select * FROM T.SC WHERE Sno ='201215126' AND Cno = '1';
SELECT * FROM T.SC_U WHERE Sno ='201215126' AND Cno = '1';

四、SQL文件

点击此处下载：SQL文件（提供数据库含表接结构和触发器源码）
提取码：ghzn