sql关联问题a\b\c三个表，
sql关联问题a\b\c三个表，a.id = b.aid 和a.id= c.a2id，这种关联如何写？
------解决思路----------------------
select a.*,b.*,c.* from a
left join b on a.id = b.aid
left join c on a.id = b. a2id
------解决思路----------------------
$user = m('a');
$user->join(left join b on a.id=b.id left join c on c.id=b.id)->field(a.id as aid,b,id as bid,……)->select();