Recursive query in SQL Server - sql

Question

I have a table with following structure
Table name: matches
That basically stores which product is matching which product. I need to process this table
And store in a groups table like below.
Table Name: groups
group_ID stores the MIN Product_ID of the Product_IDS that form a group. To give an example let's say
If A is matching B and B is Matching C then three rows should go to group table in format (A, A), (A, B), (A, C)
I have tried looking into co-related subqueries and CTE, but not getting this to implement.
I need to do this all in SQL.
Thanks for the help .

Answer 1

Try this:
;WITH CTE
AS
(
SELECT DISTINCT
M1.Product_ID Group_ID,
M1.Product_ID
FROM matches M1
LEFT JOIN matches M2
ON M1.Product_Id = M2.matching_Product_Id
WHERE M2.matching_Product_Id IS NULL
UNION ALL
SELECT
C.Group_ID,
M.matching_Product_Id
FROM CTE C
JOIN matches M
ON C.Product_ID = M.Product_ID
)
SELECT * FROM CTE ORDER BY Group_ID
You can use OPTION(MAXRECURSION n) to control recursion depth.
SQL FIDDLE DEMO

Answer 2

Something like this (not tested)
with match_groups as (
select product_id,
matching_product_id,
product_id as group_id
from matches
where product_id not in (select matching_product_id from matches)
union all
select m.product_id, m.matching_product_id, p.group_id
from matches m
join match_groups p on m.product_id = p.matching_product_id
)
select group_id, product_id
from match_groups
order by group_id;

Answer 3

Sample of the Recursive Level:
DECLARE #VALUE_CODE AS VARCHAR(5);
--SET #VALUE_CODE = 'A' -- Specify a level
WITH ViewValue AS
(
SELECT ValueCode
, ValueDesc
, PrecedingValueCode
FROM ValuesTable
WHERE PrecedingValueCode IS NULL
UNION ALL
SELECT A.ValueCode
, A.ValueDesc
, A.PrecedingValueCode
FROM ValuesTable A
INNER JOIN ViewValue V ON
V.ValueCode = A.PrecedingValueCode
)
SELECT ValueCode, ValueDesc, PrecedingValueCode
FROM ViewValue
--WHERE PrecedingValueCode = #VALUE_CODE -- Specific level
--WHERE PrecedingValueCode IS NULL -- Root