如何使用CTE映射父子关系？ [英] How to use CTE to map parent-child relationship?

问题描述

说，我有一个表，代表一个树状结构化数据，我想不断向上跟踪，直到到达顶层节点，并以parent_id为NULL标记。我的MS SQL CTE （公用表表达式）是什么样的？

Say I have a table of items representing a tree-like structured data, and I would like to continuously tracing upward until I get to the top node, marked by a parent_id of NULL. What would my MS SQL CTE (common table expression) look like?

例如，如果我要获取到达 Bender 中的顶部，看起来像是

For example, if I were to get the path to get to the top from Bender, it would look like

喜剧

Futurama

弯曲器

谢谢，这是示例数据：

DECLARE @t Table(id int, description varchar(50), parent_id int)

INSERT INTO @T 
SELECT 1, 'Comedy', null UNION 
SELECT 2, 'Futurama', 1 UNION
SELECT 3, 'Dr. Zoidberg', 2 UNION 
SELECT 4, 'Bender', 2 UNION
SELECT 5, 'Stand-up', 1 UNION
SELECT 6, 'Unfunny', 5 UNION
SELECT 7, 'Dane Cook', 6

推荐答案

看起来像这样：

declare @desc varchar(50)
set @desc = 'Bender'

;with Parentage as
(
    select * from @t where description = @desc
    union all

    select t.* 
    from @t t
    inner join Parentage p
        on t.id = p.parent_id
)
select * from Parentage
order by id asc --sorts it root-first 

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