Find Pairs in recursive table [duplicate] - sql-server

Question

This question already has an answer here:
SQL Server recursive self join
(1 answer)
Closed 5 years ago.
I have the followign table
CREATE TABLE [dbo].[MyTable2](
[ID] [int] IDENTITY(1,1) NOT NULL,
[ParentID] [int] NOT NULL,
)
I try to create a query which will return a list of pairs ID, ParentID. For example I have the followign data
ID ParentID
1 0
2 0
3 1
4 3
5 3
15 8
I want when I search by ID = 5 to have the following list:
ID ParentID
5 3
3 1
1 0
If I search by ID = 15 it should see that the sequence is boken and I will get the followign list.
ID ParentID
15 8
I used a temporary table in order to make it work and my code is the following:
if object_id('tempdb..#Pairs') is not null
DROP TABLE #Pairs
create table #Pairs
(
ID INT,
ParentID INT
)
Declare #ID integer = 5;
Declare #ParentID integer;
while (#ID > 0)
BEGIN
SET #ParentID = null; -- I set it to null so that I will be able to check in case the sequence is broken
select #ID=ID, #ParentID=ParentID
from MyTable
where ID = #ID;
if #ParentID IS NOT null
begin
Insert into #Pairs (ID, ParentID) Values (#ID, #ParentID)
SET #ID = #ParentID;
end
else
SET #ID = 0;
END
SELECT * from #Pairs
It works but I am sure that there is a better way to do it. I found some strange queries which was suspposed to do something similar but I was not able to convert it in order to cover my needs.
For example I found the following Question but I was not able to convert it to work with my table. All the queries that I found had similar answers.

Answer 1

You are looking for recursive queries. See following example:
SELECT * INTO tab FROM (VALUES
(1, 0),
(2, 0),
(3, 1),
(4, 3),
(5, 3),
(15, 8)) T(ID, ParentID);
DECLARE #whatAreYouLookingFor int = 5;
WITH Rec AS
(
SELECT * FROM tab WHERE ID=#whatAreYouLookingFor
UNION ALL
SELECT T.* FROM tab T JOIN Rec R ON R.ParentID=T.ID
)
SELECT * FROM Rec;
DROP TABLE tab
Output:
ID ParentID
-- --------
5 3
3 1
1 0