MYSQL：由两个外键从同一个表中选择

Question

我有以下表格：

航班： ID，idcompany，idplane，fromCity，toCity，起飞......

公司： ID，名称

面： ID，名称

城市： ID，名称

我想在同一个查询中声明两个城市的名称“fromCity，toCity”。

我的这个行动的目的是一次获得城市名称，所以我可以将它们展示给客户端，而不需要做另一个查询来获取城市名称。

这里是我的尝试：

SELECT f.id, f.takeoff, f.arrival, ct.name as fromCity, f.toCity, c.name as company, p.name as plane 
FROM flights f, companies c, planes p, cities ct 
WHERE f.idCompany = c.id AND f.idPlane = p.id AND f.fromCity = ct.id 
ORDER BY f.takeoff ASC 

此查询将返回“fromCity”，但“toCity”的id的名字，所以我能做些什么用相同的查询，以获得两个名字？

Answer 1

您可以使用此：

SELECT 
    f.id, f.takeoff, f.arrival, ct1.name as fromCity 
    ,ct2.name as toCity, c.name as company, p.name as plane 
FROM 
    flights f 
inner join 
    companies c 
on 
    f.idCompany = c.id 
inner join 
    planes p 
on 
    f.idPlane = p.id 
inner join 
    cities ct1 
on 
    f.fromCity = ct1.id 
inner join 
    cities ct2 
on 
    f.toCity = ct2.id 
ORDER BY 
    f.takeoff ASC; 

并尝试不使用old-style-join从现在开始。

Answer 2

你必须加入表格两次。

SELECT f.id, f.takeoff, f.arrival, ct.name as fromCity, f.toCity, c.name as company, p.name as plane , cf.name 
FROM flights f, companies c, planes p, cities ct,cities cf 
WHERE f.idCompany = c.id AND f.idPlane = p.id AND f.fromCity = ct.id AND f.toCity = cf.id 
ORDER BY f.takeoff ASC 

Answer 3

我的解决方案是使表城市的两个副本：

SELECT f.id, f.takeoff, f.arrival, ct1.name as fromCity, ct2.name as toCity, c.name as company, p.name as plane 

FROM flights f, companies c, planes p, cities ct1, cities ct2 

WHERE f.idCompany = c.id AND f.idPlane = p.id AND f.fromCity = ct1.id AND ct2.id = f.toCity 

ORDER BY f.takeoff ASC