20151016学习内容：触发器；分页语句；事务

20151016:
--触发器：一种特殊的存储过程，通过对数据库表操作的
--动作，来触发，增删改

alter trigger Fruit_Insert_After  --修改用alter
on fruit  --对哪个表操作的时候执行触发器
instead of insert -- for  --(update,delete) for的意思是动作之后触发after等同
as
    select *from inserted  --inserted临时表,就是增加的数据
go

select *from student
select *from score

delete from student where sno=101--有主外键关系

alter trigger student_delete_instead
on student
instead of delete
as
    --先删除外键表数据
    delete from score where sno in( select sno from deleted )
    --再删主键表
    delete from student where sno in (select sno from deleted)
Go



--分页语句:查询-10的数据(尽量用主键唯一查询)
select top 5 *from car order by price desc
go
select top 5 *from car where code not in (select top 5 code from car)
go
select top 5 * from car where code not in (select top 10 code from car)
go
use shujuData
go
select * from score
go
select top 5 a.sno,a.cno,a.degree from Score as a
left join (select top 5 *from Score) as b on a.sno=b.sno and a.cno=b.cno
where b.sno is null--判断是否为空is


--事务：出现错误时,会返回最开始的过程;
--保障流程的完整执行,如果一步失败就会返回到起点

select *From student
select *From score

begin tran --在流程开始的位置

    delete from student where sno=‘304‘
    delete from Student where Sno=‘303‘

if @@ERROR>0--看全局变量里是否有错误记录
begin
    rollback tran--回滚事务
end
else
begin
    commit tran--提交事务
end