SQL Server: Recursive Query

Question

I've been struggling trying to write the logic to show a relationship between interrelated records.

Here is some sample data to show what I'm trying to accomplish:

CREATE TABLE #temp_data 
(
 item_id  int,
 item_name  varchar(100),
 related_item_id  int,
 related_item_name  varchar(100)
)

INSERT INTO #temp_data 
select 10, 'apple', 20 , 'orange' UNION ALL
select 20, 'orange', 30 , 'grape' UNION ALL
select 30, 'orange', NULL , NULL UNION ALL
select 100, 'tomato', 200 , 'onion' UNION ALL
select 200, 'onion', 300 , 'tomato' UNION ALL
select 400, 'cucumber',100 , 'tomato' UNION ALL
select 300, 'pepper', NULL , NULL UNION ALL     
select 500, 'lettuce', 400 , 'cucumber' UNION ALL 
select 1000, 'beef' , NULL, NULL   UNION ALL 
select 10000, 'cheese, NULL, NULL

Expected Results:

    group_id    item_id item_name   related_item_id related_item_name
    1           10      apple       20              orange
    1           20      orange      30              grape
    1           30      orange      NULL            NULL
    2           100     tomato      200             onion
    2           200     onion       300             tomato
    2           300     pepper      NULL            NULL
    2           400     cucumber     100            tomato
    2           500     lettuce     400             cucumber
    3           1000    beef        NULL            NULL
    4           10000   cheese      NULL            NULL

I tried to accomplish this through a recursive CTE, but I had not luck.

Answer 1

Here is one solution

;WITH T AS (
    SELECT
        ROW_NUMBER() OVER (ORDER BY item_id) AS group_id,
        *
    FROM #temp_data T
    WHERE related_item_Id IS NULL 
    UNION ALL 
    SELECT T.group_id, T1.*
    FROM T
        INNER JOIN #temp_data T1
            ON T.item_id = T1.related_item_id
)

SELECT * FROM T ORDER BY group_id, item_id

The output is

group_id             item_id     item_name       related_item_id related_item_name
-------------------- ----------- --------------- --------------- -----------------
1                    10          apple           20              orange
1                    20          orange          30              grape
1                    30          grape           NULL            NULL
2                    100         tomato          200             onion
2                    200         onion           300             tomato
2                    300         pepper          NULL            NULL
2                    400         cucumber        100             tomato
2                    500         lettuce         400             cucumber