MySQL如何从友谊表中选择朋友？ [英] MySQL How to select friends from a friendship table?

问题描述

我有一个用于存储友谊的简单数据库，只有两列person_a，person_b，表示person_a和person_b是朋友。在这样的大清单中，我应该问什么查询以说出‘sam’的所有朋友。谢谢。

Hi I have a simple database for storing friendship, with just two columns person_a, person_b , denoting that person_a and person_b are friends. From a big list like this what query should I run to get say get all friends of 'sam'. Thank you.

推荐答案

使用UNION：

SELECT person_b
FROM friendship
WHERE person_a = 'sam'
UNION
SELECT person_a
FROM friendship
WHERE person_b = 'sam'

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