Select 个键由其值连接

Question

我有两列，例如键和值。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。

Answer 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，然后迭代遍历数据集，跟踪已访问的节点。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

示例数据：

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

Select 个键由其值连接

Select keys connected by its values

sql

graph-theory

recursive-query

mariadb

graph-algorithm