在SQL中加入三个表

Question

如果我想知道哪个“Mann”属于哪个“Frau”，如何加入SQL？

结果应如下所示：

FrauX "id" | MannX "id"
FrauY "id" | MannY "id" 

Answer 1

下面是联接，您可以选择查询所需的列

SELECT m.idMann
   , m.Name AS MannName
   , f.idFrau 
   , f.Name AS FrauName
FROM Mann AS m
INNER JOIN Frau_has_Mann AS fm ON m.idMann = fm.Mann_idMann
INNER JOIN Frau AS f ON fm.Frau_idFrau = f.idFrau

看起来混叠可能会造成麻烦，您可以尝试：

SELECT Mann.idMann
   , Mann.Name AS MannName
   , Frau.idFrau 
   , Frau.Name AS FrauName
FROM Mann
INNER JOIN Frau_has_Mann ON Mann.idMann = Frau_has_Mann.Mann_idMann
INNER JOIN Frau ON Frau_has_Mann.Frau_idFrau = Frau.idFrau

基本上删除了整个列名的别名。

Answer 2

Select F.idFrau,M.idMann FROM Frau AS F INNER JOIN Frau_has_Mann AS FHM ON FHM.Frau_idFrau = F.idFrau INNER JOIN Mann AS M ON M.idMann = FHM.Mann_idMann

希望这就是你要找的东西。