16、SQL基础整理（触发器.方便备份）

触发器（方便备份）

本质上还是一个存储过程，只不过不是通过exec来调用执行，而是通过增删改数据库的操作来执行（可以操作视图）

全部禁用触发器

alter table teacher disable trigger all

全部开启触发器

alter table teacher enable trigger all

create trigger TR_student_delete--默认触发器名

on student --在哪个表上操作

instead of delete --为了对表做什么而建的，‘for’是在执行完外部语句之后用，‘instead of’是直接将要执行的语句替换为执行as里面的语句

as

delete from score where sno =108

delete from student where Sno = 108

go

delete from student where Sno = 108

select *from student

108行被删掉

alter trigger TR_student_delete--默认触发器名

on student --在哪个表上操作

for delete

as

insert into student values(108,'曾鹏','男',1905-05-22,95033)

go

delete from student where Sno = 108

select *from student

*曾华变为了曾鹏

动态触发

create trigger dongtaichufa

on teacher

instead of delete

as

begin

declare @tno varchar(20)

set @tno = (select tno from deleted)—-选择执行语句中的tno所在@tno

update teacher set tname='张三'where tno = @tno

end

go

delete from teacher where Tno='831'

deleted存储删除后的信息，inserted存放更改后的信息。

执行delete语句时的tno=触发器里面的tno，而不是@tno

create trigger TR_teacher_insert

on teacher

for insert

as

begin

declare @tno varchar(20)

set @tno=(select tno from inserted)

---delete from teacher where tno=@tno

declare @sex varchar(10)

set @sex =(select tsex from teacher where tno=@tno)

if(@sex='男')

update teacher set tsex='女'where tno =@tno

else

update teacher set tsex='男'where tno =@tno

end

go

insert into teacher values (800,'王五','男',1990-09-09,'教授','计算机系')