Find the association of values in the table - sql

Question

I have one table as shown below.
Table:
LinkA linkB
--------------------
1 10
10 2
2 5
4 7
6 7
7 3
8 2
3 9
I want to find the association of values in the table. It will link to any row that has one of its two values and continue with the newly linked row.
Like that :
Row 1 (1,10) -> Row 2 (10,2) -> Row 3 (2,5) -> Row 7 (8,2). (1)
Row 4 (4,7) -> Row 5 (6,7) -> Row 6 (7,3) -> Row 8 (3,9). (2)
How to query table like that :
LinkA linkB SameLink
-------------------------------
1 10 1
10 2 1
2 5 1
4 7 2
6 7 2
7 3 2
8 2 1
3 9 2
Test table :
create table Data(
linkA INT,
linkB INT );
insert into Data(linkA, linkB)
values ('1', '10'),('10', '2'),('2', '5'),('4', '7'),('6', '7'),('7', '3'),('8', '2'),('3', '9');

Answer 1

Following Query using CTE should solve your question, just set the parameter in the first line:
DECLARE #Start AS INT = 1;
WITH CTE
AS
(
-- Case Base
SELECT LinkA, LinkB
FROM Data E1
WHERE LinkA = #Start
UNION ALL
-- Recursive Branch
SELECT C.LinkA, E2.LinkB
FROM CTE C
INNER JOIN Data E2
ON C.LinkB = E2.LinkA
)
SELECT *
FROM CTE
ORDER BY LinkA, LinkB;
More details on Tips 4 DBs

Answer 2

I created a solution based on SQL cursor
I also documented the solution for grouping related data into data islands in SQL to provide more detail about the SQL script I share below
CREATE TABLE RelatedNodes (id int identity(1,1), nodes varchar(max))
DECLARE #LinkA Int
DECLARE #LinkB Int
DECLARE #cnt Int
DECLARE #Nodes1 varchar(max)
DECLARE #Nodes2 varchar(max)
DECLARE #Id1 Int
DECLARE #Id2 Int
DECLARE sqlcursor CURSOR FAST_FORWARD FOR
select
LinkA, LinkB
from Data
Order By LinkA, LinkB
OPEN sqlcursor
FETCH NEXT FROM sqlcursor INTO #LinkA, #LinkB
WHILE ##FETCH_STATUS = 0
BEGIN
---
select
Id
into ##tblId
from RelatedNodes
where
nodes like ('%,' + convert(varchar(max),#LinkA) + ',%') or
nodes like ('%,' + convert(varchar(max),#LinkB) + ',%')
select #cnt = count(*) from ##tblId
if #cnt = 0
begin
insert into RelatedNodes
select
case when #LinkA < #LinkB
then (',' + convert(varchar(max),#LinkA) + ',' + convert(varchar(max),#LinkB) + ',')
else (',' + convert(varchar(max),#LinkB) + ',' + convert(varchar(max),#LinkA) + ',')
end
end
else if #cnt = 1
begin
update RelatedNodes
set nodes = nodes + convert(varchar(max),#LinkA) + ',' + convert(varchar(max),#LinkB) + ','
from RelatedNodes rn
inner join ##tblId t
on rn.id = t.id
end
else if #cnt = 2
begin
select top 1
#Id1 = rn.Id,
#Nodes1 = nodes
from RelatedNodes rn
inner join ##tblId t
on rn.id = t.id
order by t.id
select top 1
#Id2 = rn.Id,
#Nodes2 = nodes
from RelatedNodes rn
inner join ##tblId t
on rn.id = t.id
order by t.id desc
set #Nodes1 = #Nodes1 + #Nodes2
update RelatedNodes
set nodes = #Nodes1
where Id = #Id1
delete RelatedNodes where Id = #Id2
end
drop table ##tblId
FETCH NEXT FROM sqlcursor INTO #LinkA, #LinkB
END
CLOSE sqlcursor
DEALLOCATE sqlcursor
select
LinkA, LinkB, GroupId
from Data
inner join (
select nodes, ROW_NUMBER() over (order by id) as GroupId from RelatedNodes
) g
on g.nodes like ('%,' + convert(varchar(max),LinkA) + ',%')
Order By GroupId, LinkA, LinkB
Outcome of the execution of above SQL script is as follows providing data for all rows of sample data