sql里將重復行數據合並為一行，數據用逗號分隔

create table aa
  (
  UserID int ,
  UserName nvarchar(50),
  CityName nvarchar(50)
  );
 
 insert into aa (UserID,UserName,CityName) values (1,'a','上海')
 insert into aa (UserID,UserName,CityName) values (2,'b','北京')
 insert into aa (UserID,UserName,CityName) values (3,'c','上海')
 insert into aa (UserID,UserName,CityName) values (4,'d','北京')
 insert into aa (UserID,UserName,CityName) values (5,'e','上海')
 
 select * from aa

 
 sqlserver
 SELECT CityName,STUFF((SELECT ',' + UserName FROM aa subTitle WHERE CityName=A.CityName FOR XML PATH('')),1, 1, '') AS A
 FROM aa A
 GROUP BY CityName

 

oracle:

SELECT CityName,LISTAGG(UserName, ',') WITHIN GROUP(ORDER BY UserName) AS usernames
     FROM aa GROUP BY CityName;