Database 如何在基于子类型的查询中选择表？

我有4个表，事务，订单-超类型，然后是站点订单和产品订单子类型

[Transactions]
id PK
Orders_id [FK Orders.orders_id]

[Orders]
Orders_id PK
Orders_type

[Site_Orders]
Orders_id [FK Orders.orders_id]
== other data ==

[Product_Orders]
Orders_id [FK Orders.orders_id]
== other data ==

我的问题是，如何创建一个join语句，它将从子类型表中提取事务、关联和获取正确的信息？或者我必须使用PHP检查子类型并在那里完成逻辑

谢谢

SELECT ...
FROM Orders o
JOIN Transactions t ON t.Orders_id = o.Orders_id
LEFT OUTER JOIN Site_Orders so 
  ON so.Orders_id = o.Orders_id AND o.Orders_type = 'S' 
LEFT OUTER JOIN Product_Orders po 
  ON po.Orders_id = o.Orders_id AND o.Orders_type = 'P'