MYSQL左连接，合并字段，一对多关系操作

mysql合并字段用concat，将多个数据合并为一个字段用group_concat，切记group_concat要与group by连用，这样数据就不会只剩下一条。。。

例子：

                select
a.*, concat(
c.provencie,
c.city,
c.district,
c.location
) addressStr,
group_concat(u.userName order by u.id) rusername
from automat a
LEFT JOIN auto_addr b ON (a.id = b.aut_id)
LEFT JOIN address c ON (b.addrId = c.id)
LEFT JOIN replenishment_allocation r ON (a.id = r.autoId)
LEFT JOIN user u ON (u.id = r.userId)

group by a.id;

连接了数个表，group_concat默认连接符号是逗号，也可以使用参数修改，并且，里面可以用order by排序，简直不能再好用，记下来~