Question

我希望这不是重复，我搜索了一段时间没有任何有用的结果。

我有一个对象表（带有主键）和一个关系表。每个关系通过外键（obj_1和obj_2）引用两个对象。 obj_1和obj_2的组合是唯一的，因此我可以代表各种网络。

现在我想选择位于至少两个其他点之间的点（例如，具有多个连接）。我通过以下查询实现了这一点：

select r1.obj_1,  r1.obj_2 as hop, r2.obj_2
from t_relations r1
inner join t_relations r2 on r1.obj_2 = r2.obj_1

现在，我的问题是我希望看到每个跃点的连接数量，但是没有过滤（我需要选择所有行，因此group by不是一个选项）。我怎么能这样做？

根据要求，提供一些示例数据。为简单起见，我假设t_relations中的数字是实际对象。

t_relations

ID |  obj_1 | obj_2
 1 |   T1   |   T2
 2 |   T3   |   T2
 3 |   T4   |   T2
 4 |   T4   |   T3

预期产出：

 obj_1 |  hop |  obj_2 | count
  T1   |  T2  |   T3   |   3    # 3 connections with 2
  T3   |  T2  |   T4   |   3
  T4   |  T2  |   T1   |   3
  T4   |  T3  |   T1   |   1    # 1 connection via 3
  T2   |  T4  |   T1   |   1    # 1 connection with 4 in the middle

正如您所希望看到的那样，我希望查询“遍历”网络，采用所有可能的路由并省略重复（如1-2-4，这将是4-2-1的冗余）。我认为我的查询确实实现了这一点......计数就是问题。

Answer 1

如果我理解，每行是undirected graph的两个点之间的直接连接，并且（根据您的查询）您希望获得两个点之间的连接数一个跳。我对吗？您可以使用此查询来实现此目的（可能有一个更简单的解决方案，但这个解决方案按指定的方式工作）：

select distinct p1, tmp.hop, p2, count from (
    select if(p1 < p2, p1, p2) as p1, hop, if(p1 < p2, p2, p1) as p2 from (
        select r1.obj_1 as p1, r1.obj_2 as hop, r2.obj_2 as p2
        from t_relations r1 inner join t_relations r2 on r1.obj_2 = r2.obj_1
            union
        select r1.obj_2 as p1, r1.obj_1 as hop, r2.obj_2 as p2
        from t_relations r1 inner join t_relations r2 on r1.obj_1 = r2.obj_1
            union 
        select r1.obj_1 as p1, r1.obj_2 as hop, r2.obj_1 as p2
        from t_relations r1 inner join t_relations r2 on r1.obj_2 = r2.obj_2
            union
        select r1.obj_2 as p1, r1.obj_1 as hop, r2.obj_1 as p2
        from t_relations r1 inner join t_relations r2 on r1.obj_1 = r2.obj_2
    ) tmp where p1 <> p2
) tmp inner join (
    select hop, count(*) as count from (
        select distinct p1, hop, p2 from (
            select if(p1 < p2, p1, p2) as p1, hop, if(p1 < p2, p2, p1) as p2 from (
                select r1.obj_1 as p1, r1.obj_2 as hop, r2.obj_2 as p2
                from t_relations r1 inner join t_relations r2 on r1.obj_2 = r2.obj_1
                    union
                select r1.obj_2 as p1, r1.obj_1 as hop, r2.obj_2 as p2
                from t_relations r1 inner join t_relations r2 on r1.obj_1 = r2.obj_1
                    union 
                select r1.obj_1 as p1, r1.obj_2 as hop, r2.obj_1 as p2
                from t_relations r1 inner join t_relations r2 on r1.obj_2 = r2.obj_2
                    union
                select r1.obj_2 as p1, r1.obj_1 as hop, r2.obj_1 as p2
                from t_relations r1 inner join t_relations r2 on r1.obj_1 = r2.obj_2
            ) tmp where p1 <> p2
        ) tmp
    ) tmp group by hop
) tmp2 on tmp.hop = tmp2.hop;

MySQL：在连接后计算重复项而不进行过滤/分组

1 个答案: