sql中case when then使用实例

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