SqlServer子查询、高级

1. 子查询：把一个结果集让别人继续分析查询的就叫子查询
2. 子查询如果定义了别名，在查询引用时，必须使用别名

3. --子查询定义了别名,引用就必须用别名
   select id,n
   from Person,(select depname as n from Depment ) as d

   常用运算符：

4. in：表示对多个单列结果进行条件匹配

5. --in例子
   
   select name,age 
   from Person
   where Age in(select Age from Person where Age < 19)
   
   --any例子:与运算符结合使用,大于表示要大于查询到的结果集
   
   select name,age
   from Person
   where Age <any(select Age from Person where Age < 19)

   exists

6. --exists:判断是否为空，为空false，否则true
   
   select * from Person
   where exists(select * from Depment where id='002')
   
   
   select * from Person
   where exists(
   select * from Depment d where d.id = Person.DepID
   )

   将结果集直接在数据库插入一张新表，多数据插入

   1. --数据量多插入数据：列必须前后对应
      
      create table person3(id int primary key,name varchar(30),age int, depid varchar(20))
      
      insert into person3( id,name,age,depid)
      select ID,Name,Age,DepID from person

      更新，删除类似

7. Sql注入攻击问题，采用参数化传参形式可解决
8. 事务：保证数据原子性、一致性、隔离性、持久性
9. 开窗函数：可以对每一行结果都返回一个值，避免了group by必须分组的问题
   1. select count(*) over() from 表名

   2. select COUNT(*) over(partition by city) from shakerecode  参数意思是根据城市来分组显示出城市的数量

10. 连接池：访问数据库时所产生的链接验证成功后，当释放连接对象时，数据库就把此连接对象放到了连接池，下次使用时先从连接池找，如果连接池有这个连接对象直接使用，减少验证等消耗。
    1. 打开数据库连接对象的时间要正好，使用完连接对象要尽快释放，这样连接池的利用率高
    2. 连接字符串默认自动打开连接池，如果就想关闭连接池加语法pooling=false;
11. 子查询分页

12. --子查询分页
    --between (页码-1)*每页条数+1   and  页码*每页条数 
    select * from
    (
    select ROW_NUMBER() over(order by id) as num, * from Student
    ) t
    where t.num between (1-1)*10+1 and 1*10

     创建视图、修改视图分页

go
create view vw_student
as
select * from
(
select ROW_NUMBER() over(order by id) as num, * from Student
) t
where t.num between (1-1)*10+1 and 1*10
go

--修改视图

alter view vw_student
as
select * from
(
select ROW_NUMBER() over(order by id) as num, * from Student
) as t
go

select * from vw_student where num between 10 and 20

• 事务

--事务

--三个步骤：开始事务，提交事务，或者回滚事务

begin transaction

commit transaction

rollback transaction

set @@error  --记录最近一次数据操作的错误，如果没有错误默认是0

select @@error

• 存储过程
• 存储过程结合事务+变量+参数返回值，执行转账例子

go
create proc usp_BankToBank
@from nvarchar(10),
@to nvarchar(10),
@money money,
@issuccess int output
as
declare @myError int
set @myError = 0
begin
begin tran
update Bank set MoneyVal-=@money where ID = @from
set @myError = @myError+@@ERROR
update Bank set MoneyVal += @money where ID=@to
set @myError = @myError+@@ERROR
if @myError > 0
begin
set @issuccess = 0
rollback tran
end
else
begin
set @issuccess = 1
commit tran
end
end
go

declare @res int
exec usp_BankToBank '001','002',200,@res output
select @res

•  存储过程分页

create proc usp_StudentPage
@pageIndex int,
@pageCount int
as
begin
select * from
(
select ROW_NUMBER() over(order by id) as num,* from Student
) t
where t.num between (@pageIndex-1)*@pageCount + 1 and @pageIndex*@pageCount
end
go;

exec usp_StudentPage 2,20

•  触发器

alter trigger tr_删除触发器 on bank
after
delete
as
insert into Bank(ID,moneyval)
select * from deleted;

• 获取新增数据本身值

• -获取最近一次插入数据的值
  
  insert into Bank(ID,MoneyVal) output inserted.* values('004',20)