sql合并列

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