如何在 SQL 服务器中构建父子层次结构（从根开始）？

Question

我正在尝试使用 SQL 服务器获取从根节点到其子节点的路径。

源数据如下：

Source Data

目标应如下所示：

Target Data

由于我将在专门使用 ETL 转换的 ETL 工具中实现此功能，因此我想在不使用 CONNECT BY 等效方法的情况下实现此输出。下面的查询为我提供了结果和更多记录：

select case when level02.geography_02 is not NULL
    then '3'
    else case when level01.geography_02 is not null
                then '2'
                else case when root.geography_02 is not null
                    then '1'
                    end 
        end
end as levels,
root.geography_01 as root, root.geography_02 as super_parent,
case when level01.geography_02 is not null
        then level01.geography_02
        else ''
        end as parent,
case when level02.geography_02 is not null
        then level02.geography_02
        else ''
        end as child
from geo_table root
left join geo_table level01
on root.geography_02 = level01.geography_01
left join geo_table level02
on level01.geography_02 = level02.geography_01

请问如何获得所需的输出？

Answer 1

我认为您只需要一些过滤。也就是说，您的查询的其余部分也可以稍微简化——特别是通过使用 COALESCE():

select (case when level02.geoghraphy_02 is not NULL then '3'
             when level01.geoghraphy_02 is not null then '2'
             when root.geoghraphy_02 is not null then '1'
        end) as levels,
       root.geoghraphy_01 as root,
       root.geoghraphy_02 as super_parent,
       coalesce(level01.geography_02, '') as parent,
       coalesce(level02.geography_02, '') as child
from geo_table root left join
     geo_table level01
     on root.geography_02 = level01.geography_01 left join
     geo_table level02
     on level01.geography_02 = level02.geography_01
where not exists (select 1
                  from geo_table gt
                  where gt.geography_02 = root.geography_01
                 );

基本上，您只需要将 "root" 限制为实际的根记录。您实际上已经处理了逻辑中比较棘手的部分（在我看来）。

如何在 SQL 服务器中构建父子层次结构（从根开始）？

How to build parent-child hierarchies (starting from root) in SQL Server?

sql

sql-server

parent-child

sql-server-2017