获取完整层次结构路径的 SQL 查询

问题描述

我有一个包含三列 NodeId、ParentNodeId 和 NodeName 的表.对于每个节点，我想获得一个完整的路径，如lvl1/lvl2/lvl3..."，其中 lvl1、lvl2 和 lvl3 是节点名称.我在此链接中找到了一个函数 http://www.sql-server-helper.com/functions/get-tree-path.aspx.但我想使用 CTE 或任何其他技术来提高效率.请让我知道是否有可能以更好的方式实现这一目标.提前致谢.

I have a table with three columns NodeId, ParentNodeId, NodeName. for each node I would like to get a full path like "lvl1/lvl2/lvl3..." where lvl1,lvl2 and lvl3 are node names. I found a function which does that at this link http://www.sql-server-helper.com/functions/get-tree-path.aspx. but I would like to use CTE OR any other technique for efficiency. Please let me know if it is possible to achieve this in a better way. Thanks in advance.

推荐答案

这是 CTE 版本.

declare @MyTable table (
    NodeId int,
    ParentNodeId int,
    NodeName char(4)
)

insert into @MyTable
    (NodeId, ParentNodeId, NodeName)
    select 1, null, 'Lvl1' union all
    select 2, 1, 'Lvl2' union all
    select 3, 2, 'Lvl3'

declare @MyPath varchar(100)

;with cteLevels as (
    select t.NodeId, t.ParentNodeId, t.NodeName, 1 as level
        from @MyTable t
        where t.ParentNodeId is null
    union all
    select t.NodeId, t.ParentNodeId, t.NodeName, c.level+1 as level
        from @MyTable t
            inner join cteLevels c
                on t.ParentNodeId = c.NodeId
)
select @MyPath = case when @MyPath is null then NodeName else @MyPath + '/' + NodeName end
    from cteLevels
    order by level

select @MyPath