SQL Sever中使用SQL语句实现把重复行数据合并为一行并用逗号分隔

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
group by cityname

----第二种方式
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：