CODEWITHSUNDEEP
sql-serverhierarchycommon-table-expression
Haoest
Haoest

Reputation: 13906

How to use CTE to map parent-child relationship?

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?

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

Comedy

Futurama

Bender

Thanks, and here's the sample data:

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

Upvotes: 3

Views: 4262

Answers (1)

dan
dan

Reputation: 9852

it should look like this:

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

Upvotes: 4

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