Question

是否可以将 table a 中的列与 table b 中的2列连接起来？

以下是我的情况的一个简单示例：

**Flight**
  idFlight     Flightnumber     Date          idDepart    idArrival
  1            5871             2018-02-03    1           2
  2            5872             2018-03-08    1           3
  3            5873             2018-03-19    3           2
  4            5874             2018-04-11    2           1
  5            5875             2018-04-21    3           2

**Airport**
  idAirport     Code     Name
  1             AMS      Amsterdam Airport Schiphol
  2             JFK      John F Kennedy International Airport
  3             TXL      Berlijn Tegel Airport

我想要完成的是在一个查询中概述航班的起飞和到达地点。这是我到目前为止所得到的：

SELECT Flight.Flightnumber, Flight.Date, Airport.Name AS 'Arriving at' FROM Flight
LEFT JOIN Airport ON Flight.idArrival = Airport.idAirport

但似乎无法弄明如何在Flight.idDepart上Airport.idAirport创建另一个别名“离开”。两次加入机场不起作用所以我尝试使用这样的子查询：

SELECT Flight.Flightnumber, Flight.Date, Airport.Name AS 'Arriving at',
    ( SELECT Airport.Name AS 'Departing from' FROM Flight
        LEFT JOIN Airport ON Flight.idDepart = Airport.idAirport ) 
    FROM Flight
LEFT JOIN Airport ON Flight.idArrival = Airport.idAirport

实现这一目标的最佳方式是什么？

Answer 1

您可以尝试两个左边的连接，机场1用于出发，1个用于到达，

尝试以下查询。

SELECT 
f.Flightnumber, 
f.date, 
a.name AS dept, 
a1.name AS arrvl 
FROM 
flight f LEFT JOIN airport a ON a.idAirport = f.idDepart 
LEFT JOIN airport a1  ON a1.idAirport = f.idArrival

尝试演示Here

Answer 2

这可以为您提供您正在寻找的结果集：

SELECT f.FlightNumber, f.FlightDate, d.Name AS departAirport, a.Name AS arrivalAirport
FROM Flight AS f
LEFT JOIN Airport AS d ON f.idDepart = d.idAirport
LEFT JOIN Airport AS a ON f.idArrival = a.idAirport

Answer 3

您可以对每个查询进行别名，如下所示（ 未经测试 ）：

SELECT flights.FlightNumber, flights.FlightDate, departures.Name, arrivals.Name 
FROM (SELECT * FROM Flight) AS flights 
LEFT JOIN (SELECT * FROM Airport) AS departures ON flights.idDepart = departures.idAirport
LEFT JOIN (SELECT * FROM Airport) AS arrivals ON flights.idArrival = arrivals .idAIrport

Answer 4

尝试相关的子查询

   SELECT Flight.Flightnumber, Flight.Date, Airport.Name AS 'Arriving at',
        ( SELECT Airport.Name from Airport ON Flight.idDepart = Airport.idAirport) as 'Departing From'
    FROM Flight
    JOIN Airport ON Flight.idArrival = Airport.idAirport

多条件JOIN ON列？

4 个答案: