sql将数据按照某一列合并

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

sql合并两列数据：
CONCAT(str1,str2,…)
select CONCAT(str1,"–",str2,…) from table