sql里將重復行數據合並為一行，數據用逗號分隔

一.定義表變量

DECLARE @T1 table
(
UserID int , 
UserName nvarchar(50),
CityName nvarchar(50)
);

insert into @T1 (UserID,UserName,CityName) values (1,'a','上海')
insert into @T1 (UserID,UserName,CityName) values (2,'b','北京')
insert into @T1 (UserID,UserName,CityName) values (3,'c','上海')
insert into @T1 (UserID,UserName,CityName) values (4,'d','北京')
insert into @T1 (UserID,UserName,CityName) values (5,'e','上海')

select * from @T1

-----最優的方式
SELECT CityName,STUFF((SELECT ',' + UserName FROM @T1 subTitle WHERE CityName=A.CityName FOR XML PATH('')),1, 1, '') AS A
FROM @T1 A
GROUP BY CityName

----第二種方式
SELECT B.CityName,LEFT(UserList,LEN(UserList)-1) 
FROM (
  SELECT CityName,(SELECT UserName+',' FROM @T1 WHERE CityName=A.CityName FOR XML PATH('')) AS UserList
  FROM @T1 A 
  GROUP BY CityName
     ) B

stuff(select ',' + fieldname  from tablename for xml path('')),1,1,'')
這一整句的作用是將多行fieldname字段的內容串聯起來，用逗號分隔。

for xml path是SQL Server 2005以后版本支持的一種生成XML的方式。

stuff函數的作用是去掉字符串最前面的逗號分隔符。