在两个表之间如何选择一个特定值的id所在的表存在mysql [英] Between two tables how does one SELECT the table where the id of a specific value exists mysql

问题描述

在我的Hiking数据库中有两个表，我们称表1被称为Forest，表2被称为Mountain。两个表在表Trip中都有一个 FOREIGN KEY Trip_id，它是一个 PRIMARY KEY 是一个组成的例子）是 AUTO_INCREMENT 。

I have 2 tables in my "Hiking" database lets say table 1 is called "Forest" and table 2 is called "Mountain". Both tables have a FOREIGN KEY "Trip_id" which is a PRIMARY KEY in table "Trip" (or something, this is a made up example) that is AUTO_INCREMENT. A trip can either be Mountain or Forest, so the 2 tables do not share any Trip_ids.

我想要 SELECT * FROM 取决于哪一个具有某个值的 Trip_id （让我们说74）的森林或山。

I want to SELECT * FROM either Forest or Mountain depending on which one has the Trip_id of a certain value (lets say 74).

SELECT * FROM FOREST OR MOUNTAIN WHERE Trip_id = 74 EXISTS; 

（我知道这个代码是垃圾和完全错误，但我希望它有助于说明我的目标）。

(I know this code is rubbish and completely wrong but I hope it helps illustrate what I am aiming for).

推荐答案

假设它们有相同的列，那么使用 union all ：

Assuming they have the same columns, then use union all:

select m.*
from mountains m
where m.trip_id = 74
union all
select f.*
from forests f
where f.trip_id = 74;

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