表A中一条记录的两个字段都对应于表B的同一个字段 如何查询？SQL, thinkphp[5]

表  A=approval_order, B=admin,  表A中technician_username, salesman_username 都是id号，中文名保存在admin表的nickname字段

ThinkPHP代码：

$row = db('approval_order')->alias('ao')
            ->field('a1.nickname as technician,a2.nickname as salesman,ao.*')
            ->join('admin a1','ao.technician_username=a1.username')
            ->join('admin a2','ao.salesman_username=a2.username')
            ->where('ao.id','=',$id)
            ->find();

SQL代码：（表名懒得改了，谷歌找到的）

select t1.team_name as team1, t2.team_name as team2, t.team_1, t.team_2
from trades t
inner join teams t1 on t1.id = t.team_1
inner join teams t2 on t2.id = t.team_2;