只有当 id_user_a 和 id_user_b 与给定用户id 匹配时才需要选择用户 。
users // SQL Statements: http://pastebin.com/w34qQv0g
id username
1 user1
2 user2
3 user3
4 user4
matches
id_user_a id_user_b
1 2
2 1
1 4
4 1
如上文所示,对于给定的用户 ID 1, 匹配表格中双向匹配的 id s id 是 id=2 和 id=4。 因为第一个匹配为 II 和 反之 (1-2 和 2-1 * 1-4 和 4-1) 。
对于给定的 ID 4, 只需要一个双向匹配的id(1-4 和 4-1), 然后只有双向匹配的 id=1 和 id 4 。 我想为给定的 id 选择双向匹配的 id s。 这个概念相当清楚, 不是吗? 但是, 在选择的语句中我怎么能做到这一点呢? 有人能帮我吗? 谢谢。
日期 4 :
SELECT
distinct m1.id_user_b
FROM
MATCHES M1
JOIN MATCHES M2 ON M1.ID_USER_A = M2.ID_USER_B AND M2.ID_USER_A = M1.ID_USER_B
WHERE M1.ID_USER_A = 4
将4改为参数。
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