Question

我有三个表A，B和C

表A和B具有ID和其他字段，表C是A和B的n-n关系（C仅包含具有主键（id_a，id_b）和外键的A和B的IDS）。

现在，我需要验证A的一行是否与A的另一行具有相同的关联性。

示例

A = [id_a] = [1,2,3,4]
B = [id_b] = [1,2,3,4]

C = [id_a, id_b] = [[1,1],[1,3],[2,1],[2,3],[3,3]]

在这种情况下，我只需要提取id_a为1和2的记录，因为它们都与B的同一行（id_b 1和3）相关联。

id_a = 3与id_a = 1/2不同，因为它与id_b = 1没有关联

这用于运行MySQL，PHP 7（LAMP堆栈）的新Ubuntu 18.04服务器

id_a = 1的示例

SELECT id_a
FROM C
WHERE id_b IN (SELECT id_b FROM B WHERE id_a=1)
GROUP BY id_a;

Answer 1

精确匹配的最简单方法是使用group_concat()：

select c.id_a
from (select c.id_a, group_concat(c.id_b order by c.id_b) as id_bs
      from c
      group by c.id_a
     ) c join
     (select group_concat(c.id_b order by c.id_b) as id_bs
      from c
      where c.id_a = @id_a
     ) ac
     on c.id_bs = ac.id_bs

比较n-n关系的所有记录

1 个答案: