如何基于其他表中的其他关系从1列中选择2个数据

Question

说，我有一个类似以下的表格，称为“名称”：

| nid | name   |
----------------
| 1   | john   | 
| 2   | mike   | 
| 3   | tom    |
| 4   | jack   |
| 5   | will   |
| 6   | david  | ...

和另一个类似以下的表，称为“ relation_father_son”：

| rid | fnid | snid |
---------------------
| 1   |    1 |    2 |
| 2   |    1 |    3 |
| 3   |    4 |    5 |
| 4   |    2 |    6 | ...

然后我想要一个类似以下的结果：

| father | son   |
------------------
| john   | mike  |
| john   | tom   |
| jack   | will  |
| mike   | david | ...

SQL查询应该是什么？

Answer 1

查询为：

SELECT 
  f.name AS father, 
  s.name AS son
FROM relation_father_son 
INNER JOIN name AS f 
  ON (nid = fnid)
INNER JOIN name AS s 
  ON (nid = snid)

Answer 2

首先，将第一个表命名为name令人困惑。您应该将其重命名为更专有的名称，例如family_names。要了解更多信息，请访问：Is name a reserved word in MySQL?

要获得所需结果，可以使用以下查询：

SELECT 
  (SELECT `name` FROM `family_names` WHERE nid=fnid) AS father, 
  (SELECT `name` FROM `family_names` WHERE nid=snid) AS son 
FROM relation_father_son