将多行数据合并为一行

oracle语法：
  select country,wmsys.wm_concat(city) as city from test group      bycountry

 

mysql语法：
select country,GROUP_CONCAT(city order by city separator",") as city from test GROUP BY country

 

sqlserver语法：
select country,sys_connect_by_path(city,',') as city from test

 

效果如图所示：