sql里将重复行数据合并为一行，数据用逗号分隔

一.定义表变量

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

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

----第二种方式

SELECT   CityName ,
                REPLACE(RTRIM(REPLACE(REPLACE(( SELECT  UserName
                                                FROM    @T1 m
                                                where    m.CityName = A.CityName
                                                 FOR XML AUTO
                                              ), '<m UserName="', ''), '"/>',
                                      ' ')), ' ', ',')
       FROM     @T1 A

----第三种方式
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,'')
这一整句的作用是将多行fieldname字段的内容串联起来，用逗号分隔。

for xml path是SQL Server 2005以后版本支持的一种生成XML的方式。

stuff函数的作用是去掉字符串最前面的逗号分隔符。

效果图：