SQL语句 合并列值 将一列的多个值合并成一行

oralce写法：
select WM_CONCAT(A.title) as citys from tmpcity A

sql server写法：
select stuff((select ','+A.title from tmpCity A FOR xml PATH('')), 1, 1, '') as citys

mysql写法：
select GROUP_CONCAT(A.title) as citys from tmpcity A; --默认的逗号分隔

select GROUP_CONCAT(A.title SEPARATOR ' ') as citys from tmpcity A; --用空格分隔