database - 规范化 - 重复外键

Question

规范化数据时，是否可以接受在同一张表中重复使用外键？

例如一家 express 公司有一个订单表和一个客户表，订单表会记录从哪个客户那里取件(Customer_ID)，并且还会有一列用于说明要交付给哪个客户(也是 Customer_ID)。

Answer 1

完全可以接受；这两个索引将分开维护。这两个关系可以分开使用...

select item, name, address from orders inner join customers on orders.sender = customers.id where orders.id = 5;
select name, address from orders inner join customers on orders.recipient = customers.id where orders.id = 5;

或一起(小心)

select item, name as sender_name, address as sender_address, recipients.name as as recipient_name, recipients.address as recipient_address from orders inner join customers on orders.sender = customers.id inner join customers as recipients on orders.recipient = recipients.id;

做小心级联删除；)