选择按其值连接的键答案

【问题标题】：Select keys connected by its values选择按其值连接的键
【发布时间】：2020-12-01 19:53:49
【问题描述】：

我有两列，比如键和值。我需要关于值之间连接的组键，如图所示。相同的值连接键。我不知道该怎么做。使用 10.5.8-MariaDB。

【问题讨论】：

标签： sql mariadb graph-theory graph-algorithm recursive-query

【解决方案1】：

这是一个典型的图遍历问题 - 需要递归查询，从 MariaDB 10.2.2 开始可用。

这是一种方法，首先将边构建为连接节点的元组，然后迭代地遍历数据集，跟踪已经访问过的节点。我们可以通过跟踪最小访问节点来识别每个节点属于哪个组。

with recursive 
    edges as (
        select t1.lagr_number as lagr_number1, t2.lagr_number as lagr_number2
        from mytable t1
        inner join mytable t2 on t2.ltran_number = t1.ltran_number
    ),
    cte as (
        select lagr_number1, lagr_number2, concat(lagr_number1, ',', lagr_number2) as visited
        from edges
        union all
        select c.lagr_number1, e.lagr_number2, concat(c.visited, ',', e.lagr_number2)
        from cte c
        inner join edges e on e.lagr_number1 = c.lagr_number2
        where not find_in_set(e.lagr_number2, c.visited)
    )
select lagr_number1 as lagr_number, dense_rank() over(order by min(lagr_number2)) as grp
from cte
group by lagr_number1
order by grp, lagr_number1

Demo on DB Fiddle

样本数据：

lagr_number | ltran_number :------------ | :----------- K000001 | V000001 K000001 | V000004 K000001 | V000005 K000002 | V000001 K000003 | V000002 K000003 | V000003 K000004 | V000005 K000005 | V000007 K000005 | V000008 K000006 | V000009 K000007 | V000009

结果：

lagr_number | grp :------------ | --: K000001 | 1 K000002 | 1 K000004 | 1 K000003 | 2 K000005 | 3 K000006 | 4 K000007 | 4

【讨论】：