sql中case when then使用实例

CREATE TABLE [Test] (

[id] [int] IDENTITY (1, 1) NOT NULL ,

[name] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NULL ,

[subject] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NULL ,

[Source] [numeric](18, 0) NULL

) ON [PRIMARY]

GO

INSERT INTO [test] ([name],[subject],[Source]) values (N'张三',N'语文',60)

INSERT INTO [test] ([name],[subject],[Source]) values (N'李四',N'数学',70)

INSERT INTO [test] ([name],[subject],[Source]) values (N'王五',N'英语',80)

INSERT INTO [test] ([name],[subject],[Source]) values (N'王五',N'数学',75)

INSERT INTO [test] ([name],[subject],[Source]) values (N'王五',N'语文',57)

INSERT INTO [test] ([name],[subject],[Source]) values (N'李四',N'语文',80)

INSERT INTO [test] ([name],[subject],[Source]) values (N'张三',N'英语',100)

Go

select * from dbo.test

--交叉表语句的实现：

--1.用于：交叉表的列数是确定的

select name,

sum(case subject when '数学' then source else 0 end) as '数学',

sum(case subject when '英语' then source else 0 end) as '英语',

sum(case subject when '语文' then source else 0 end) as '语文'

from test

group by name

--2.用于：交叉表的列数是不确定的

declare @sql varchar(8000)

set @sql = 'select name,'

select @sql = @sql + 'sum(case subject when '''+subject+'''

then source else 0 end) as '''+subject+''','

from (select distinct subject from test) as a

select @sql = left(@sql,len(@sql)-1) + ' from test group by name'

exec(@sql)

go

--3.用于：交叉表的列数是不确定的

declare @sql varchar(8000)

set @sql = 'select id,name,'

select @sql = @sql + '(case subject when '''+subject+'''

then source else null end) as '''+subject+''','

from (select distinct subject from test) as a

select @sql = left(@sql,len(@sql)-1) + ' from test '

exec(@sql)

go