选择链接到第三个表中的数据的行

Question

我有三张桌子A，B，C

在表A中，我有一个coloumn unit_id

unit_id  id 
3456     45678

表B中有两个coloumn id和project_id

id             project_id
3456           4567

在第三张表C中，我又有两个颜色

project_id     user_id
4567           36547

我想要一个函数，我只输入表A中的id，它给我表C中对应于该unit_id的User_id

Answer 1

假设每个unit_id始终只有一个对应的user_id：

SELECT A.`unit_id`, C.`user_id` 
FROM A INNER JOIN B ON A.`unit_id` = B.`id` 
INNER JOIN C ON B.`project_id` = C.`project_id`

修改

SELECT C.`user_id` 
FROM A INNER JOIN B ON A.`unit_id` = B.`unit_id` 
INNER JOIN C ON B.`project_id` = C.`project_id`
where A.id= [your id]