php - Mysql SELECT 好友系统

Question

我有这张桌子

conncections

id_user connectedto
    1       4
    2       4
    3       1
    1       5

我想做一个SELECT返回所有与数字 1 和数字 1 本身有关的数字。因此1 4 3 5作为结果。

Answer 1

就像是

SELECT DISTINCT id_user as related
FROM connections
WHERE connectedto = 1
UNION
SELECT DISTINCT  connectedto as related
FROM connections
WHERE id_user = 1

删除了 UNION 重复项