多个全外连接

Question

我想将 a 的结果FULL OUTER JOIN用作FULL OUTER JOIN另一个表的表。我应该使用什么语法？

例如：T1、T2、T3 是我的带有 id、name 列的表。我需要类似的东西：

T1 FULL OUTER JOIN T2 on T1.id = T2.id   ==> Let this be named X

X FULL OUTER JOIN T3 on X.id = t3.id  

我希望实现这一点，以便在最后的 ON 子句中，我希望 T3.id 匹配T1.id或T2.id。任何替代方法也可以。

Answer 1

SELECT COALESCE(X.id,t3.id) AS id, *-- specific columns here instead of the *
FROM 
    (
       SELECT COALESCE(t1.id,t2.id) AS id, * -- specific columns here instead of the *
       FROM T1 FULL OUTER JOIN T2 on T1.id = T2.id
    ) AS X
    FULL OUTER JOIN T3 on X.id = t3.id