mssql trigger

create database TestTriggerDb 
go
use TestTriggerDb
go

create table Student
(
    StuId char(4) primary key,
    StuName varchar(10)
)
go
create table Score
(
    StuId char(4),
    WrittenExam numeric(5,2),
    LabExam  numeric(5,2)
)

insert student values('1101','张1')
insert student values('1102','张2')
insert student values('1103','张3')
insert student values('1104','张4')

insert Score values('1101',rand()*101,rand()*101)
insert Score values('1102',rand()*101,rand()*101)
insert Score values('1103',rand()*101,rand()*101)
insert Score values('1104',rand()*101,rand()*101)

select * from student
select * from score
------------------
--触发器可以分两种：
--1，after trigger 2， instead of trigger
--区别是after trigger是实际操作完成后触发，
--而instead of是实际操作前触发，并且会替换实际操作，
--也就是说触发instead of 之后实际操作将不会再执行
------------------

--创建触发器
if exists(select * from sysobjects where name=N'trigger_Stu_stuId')
    drop trigger trigger_Stu_stuId
go
create trigger  trigger_Stu_stuId
on student
instead of update,delete
as
    if update(StuId)
        begin
            update Score set score.StuId=i.StuId
            from Inserted i,Deleted d
            where score.StuId=d.StuId
        end
print 'trigger'
go

--test sql:
update student set stuId=1105 where stuId=1101

--update student set stuId=1101 where stuId=1105


select * from student
select * from score


--结果如下：

StuId StuName
----- ----------
1101  张1
1102  张2
1103  张3
1104  张4

(4 行受影响)

StuId WrittenExam                             LabExam
----- --------------------------------------- ---------------------------------------
1105  74.43                                   78.52
1102  52.48                                   42.06
1103  95.48                                   43.14
1104  86.82                                   12.85
1105  94.87                                   25.20
1102  91.43                                   4.74
1103  29.82                                   84.51
1104  42.66                                   27.91
1105  31.53                                   66.85
1102  32.63                                   64.26
1103  81.22                                   64.88
1104  76.14                                   80.34
1105  1.82                                    58.37
1102  51.98                                   73.34
1103  61.74                                   77.99
1104  91.15                                   75.50

--从结果可以看出，触发器已经成功更新了score 表，但student表的更新没有执行，
--主要是被instead of 触发器替换了

--接下来再把表恢复到原来状态
update score set stuId=1101 where stuId=1105
select * from student
select * from score

--结果如下，部分省略
StuId StuName
----- ----------
1101  张1
1102  张2
1103  张3
1104  张4

(4 行受影响)

StuId WrittenExam                             LabExam
----- --------------------------------------- ---------------------------------------
1101  74.43                                   78.52
1102  52.48                                   42.06
1103  95.48                                   43.14
1104  86.82                                   12.85
1101  94.87                                   25.20

--
--创建after触发器
if exists(select * from sysobjects where name=N'trigger_Stu_stuId')
    drop trigger trigger_Stu_stuId
go
create trigger  trigger_Stu_stuId
on student
after update,delete--在这里指定触发器类型和触发条件
as
    if update(StuId)
        begin
            update Score set score.StuId=i.StuId
            from Inserted i,Deleted d
            where score.StuId=d.StuId
        end
print 'trigger'
go

--test sql:
update student set stuId=1105 where stuId=1101
select * from student
select * from score

--结果如下：
StuId StuName
----- ----------
1102  张2
1103  张3
1104  张4
1105  张1

(4 行受影响)

StuId WrittenExam                             LabExam
----- --------------------------------------- ---------------------------------------
1105  74.43                                   78.52
1102  52.48                                   42.06
1103  95.48                                   43.14
1104  86.82                                   12.85
1105  94.87                                   25.20
--从结果可以看出，两个表都更新成功