加入2列同桌另一列

Question

我想加入2列，在另一個表

這裏分享相同的外鍵的表：

country: 
idcountry| countryname 
1   german 
2   america 

目的地

id|fromcountry |tocountry 
1 1    2 

結果我想：

id|fromc |toc 
1 german america 

Answer 1

使用左外連接這兩個領域 像這樣

SELECT Dest.ID, CFrom.CountryName, CTo.CountryName 
FROM Destination Dest 
LEFT OUTER JOIN Country CFrom ON Dest.FromCountry = CFrom.idcountry 
LEFT OUTER JOIN Country CTo ON Dest.ToCountry = CTo.idcountry 

Answer 2

使用簡單LEFT JOIN ANS以國家名稱列提供別名：

SELECT d.idcountry as id, cf.CountryName as fromc, ct.CountryName as toc 
FROM destination d 
LEFT JOIN country cf ON d.fromcountry = cf.idcountry 
LEFT JOIN country ct ON d.tocountry = ct.idcountry