题解 | #返回产品名称和与之相关的订单号#

select prod_name,order_num
from Products p left join OrderItems o on p.prod_id=o.prod_id
union
select prod_name,order_num
from Products p right join OrderItems o on p.prod_id=o.prod_id
order by prod_name;

MySQL 没有outer join 所以要左右一起用， union 自动去重