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CTE to list all children per node in hierarchy

ParentChildTb
ID    Parent
004  003
003  002
002  001
001  001
Desired Output:
Parent Child
001  002
001  003
001  004
002  003
002  004
003  004
I need a query that traverses through a tree and gets all children, grandchildren, etc. per item
Each item can have many children on different levels and each child can have multiple parents.

Thank you!
0
larisa1970
Asked:
larisa1970
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1 Solution
 
Guy Hengel [angelIII / a3]Billing EngineerCommented:
this should do:
with data as (
  select id, parent from ParentChildTb t where not exists ( select null from ParentChildTb x where x.id = t.Parent )
 UNION ALL
 select t.id, t.parent from ParentChildTb t join data on data.id = t.parentid
)
select * from data

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0
 
larisa1970Author Commented:
Angelll,
thanks, but you query doesn't return anything.
It should return more records than in the original table
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Guy Hengel [angelIII / a3]Billing EngineerCommented:
sorry, I see:
with data as (
  select id, parent from ParentChildTb t where id = parent)
 UNION ALL
 select t.id, t.parent from ParentChildTb t join data on data.id = t.parentid
)
select * from data

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larisa1970Author Commented:

"The statement terminated. The maximum recursion 100 has been exhausted before statement completion."
0
 
SharathData EngineerCommented:
check this.
-- @ParentChildTb1 is your main table
declare @ParentChildTb1 table(ID int,Parent int)
insert @ParentChildTb1 values(4,3)
insert @ParentChildTb1 values(3,2)
insert @ParentChildTb1 values(2,1)
insert @ParentChildTb1 values(1,1)

-- Create a temp table, insert all the records from your main table and update the rool to NULL 
declare @ParentChildTb table(ID int,Parent int)
insert @ParentChildTb select * from @ParentChildTb1
update @ParentChildTb set Parent = NULL where ID = Parent

-- Try this CTE to get the Tree of parents
;WITH cte AS(
SELECT ID, Parent, coalesce(Convert(varchar(max),Parent)+',','') AS Tree
  FROM @ParentChildTb
 WHERE Parent is null
 UNION ALL
SELECT c.ID, c.Parent, p.Tree + ',' + CAST(c.Parent AS varchar(max))
  FROM @ParentChildTb c
  JOIN cte p
    ON c.Parent = p.ID
),cte2 as (
SELECT ID,Parent,SUBSTRING(Tree,2,LEN(Tree)) Tree FROM cte)
-- This query gives the desired output
select ParentID,ID ChildID from (
SELECT ID,ltrim(SUBSTRING(Tree, n, CHARINDEX(',', Tree + ',',n) - n)) AS ParentID
 FROM cte2
CROSS JOIN (SELECT number FROM master..spt_values WHERE type = 'P')  AS Numbers(n)
WHERE SUBSTRING(',' + Tree, n, 1) = ','
  AND n < LEN(Tree) + 1) t1
order by ParentID,ID
/*
ParentID	ChildID
1	2
1	3
1	4
2	3
2	4
3	4
*/

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Guy Hengel [angelIII / a3]Billing EngineerCommented:
of course...
with data as (
  select id, parent from ParentChildTb t where id = parent)
 UNION ALL
 select t.id, t.parent from ParentChildTb t join data on data.id = t.parentid and t.id <> t.parentid
)
select * from data

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SharathData EngineerCommented:
I am not sure why did you accept http:#34892392. First thing is there are syntactical errors in that query. Forget about syntax errors. The query is not producing the expected result.
declare @ParentChildTb1 table(ID int,Parent int)
insert @ParentChildTb1 values(4,3)
insert @ParentChildTb1 values(3,2)
insert @ParentChildTb1 values(2,1)
insert @ParentChildTb1 values(1,1)

;with data as (
  select id, parent from @ParentChildTb1 t where id = parent
 UNION ALL
 select t.id, t.parent from @ParentChildTb1 t join data on data.id = t.Parent and t.id <> t.Parent
)
select * from data
/*
id	parent
1	1
2	1
3	2
4	3
*/

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SharathData EngineerCommented:
I would suggest Option #3: Accept one or more comments as the solution.The correct answer would be http:#a34890907
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Guy Hengel [angelIII / a3]Billing EngineerCommented:
well, when I analyse the question in deep, even Sharath's code will not solve all the scenarios properly without an additional distinct.

>Each item can have many children on different levels and each child can have multiple parents.
this was not in the test case neither, and will result in duplicates.

I presumed the asker was happy with the simple code ...


so my suggestion would be to split between the original accepted comment and Sharath's comment
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