caseend 和子查询

MSSQL操作 case end 和子查询 代码如下：

create database Test
go
use Test
go
create table [user]
(
    uId int identity(1,1) primary key,
    name varchar(50),
    level int  --1骨灰 2大虾 3菜鸟
)
go
insert into [user] (name,level) values('犀利哥',1)
insert into [user] (name,level) values('小月月',2)
insert into [user] (name,level) values('芙蓉姐姐',3)

select * from [user]

--1、case end 相当于c#中的swith
select [name],
    case [level] 
        when 1 then '骨灰' 
        when 2 then '大虾'
        when 3 then '菜鸟'
        else '神仙'
    end as '等级'
from [user]

--2、case end 相当于c#的多重if语句
--注意：case end的返回值类型要一致
use MySchool

select * from score

select studentId,
    case
        when english >=90 and english <=100 then 'A'
        when english between 80 and 89 then 'B'
        when english between 70 and 79 then 'C'
        when english between 60 and 69 then 'D'
        else 'E'
    end
from score

--练习1
select 
    case 
        when a>b then a
        else b
    end,
    case 
        when b > c then b
        else c
    end
from biao


select abs(-39)

--练习2
use Test
go
create table test
(
    number varchar(10),
    amount int
)
insert into test(number,amount) values('RK1',10)
insert into test(number,amount) values('RK2',20)
insert into test(number,amount) values('RK3',-30)
insert into test(number,amount) values('RK4',-10)
go

select * from test

select number,
    case
        when amount > 0 then amount
        else 0
    end as 收入,
    case 
        when amount < 0 then abs(amount)
        else 0
    end as 支出
from test

--增加练习
name sex -- 0 1 
select name,
    case sex
        when 1 then '男'
        when 0 then '女'
    end 
from student
--练习3
use Test
go
CREATE TABLE student0 (name nvarchar(10),subject nvarchar(10),result int)
INSERT INTO student0 VALUES ('张三','语文',80)
INSERT INTO student0 VALUES ('张三','数学',90)
INSERT INTO student0 VALUES ('张三','物理',85)
INSERT INTO student0 VALUES ('李四','语文',85)
INSERT INTO student0 VALUES ('李四','数学',92)
INSERT INTO student0 VALUES ('李四','物理',null)

SELECT * FROM student0

select name,
    sum(case subject
        when '语文' then result
    end) as '语文',
    sum(case subject 
        when '数学' then result
    end) as '数学',
    isnull(sum(case subject
        when '物理' then result
    end),0) as '物理'
from student0
group by name

--isnull(,)



use MySchool
select * from student

select * from [user]
delete from [user] where uid in (7,8,9)
insert into [user] (uUserName,uPwd,uTimes) values('123','123',0)
select * from [user]



--子查询
select * from (select * from student where sAge<23) as t

--
select max(english) from score
union all
select min(english) from score
union all
select avg(english) from score

select (select max(english) from score) as t,
(select min(english) from score),
(select avg(english) from score)

--查询高二一班所有的学生
select * from class
select * from student

--当=、!=、<、<=、>、>=号后面是子查询的时候，
--子查询必须返回一列
--子查询必须返回一行
--错误的情况，因为子查询返回多行
select * from student where sClassId=
(select cId from class where cName='高二一班' or cName='高二二班')


--查询所有高二的学生
select * from student where sClassId in 
(select cId from class where cName like '高二%')

--查询刘关张 的成绩
select * from score where studentId in
(select sId from student where sName in ('曹操','夏侯惇','张飞'))

--子查询删除数据
delete from score where studentId in 
(select sId from student where sName in ('曹操','夏侯惇') )

select * from score

--分页

select top 5 * from student order by sId desc
--查询最近插入的第6-10个人。除了前5个人的前5条
select top 5 * from student where sId not in
(select top (5*(3-1)) sId from student order by sId desc)
order by sId desc

--sql 2005以后生成连续的编号
insert into student (sName,sSex,sAge) values('abc','男',18)

select row_number() over(order by sId desc),*
from student

select * from 
(select *,row_number() over(order by sId desc) as [no] from student) as t
where t.[no] between (5*(3-1))+1 and (5*3)
order by sId desc


select * from student