Merge or join two tables SQL Server

Question

I have a table with two columns Item , Qty and another table with Product , Quantity .

Table A

Item	Qty
a	10
a	15
a	5
b	10

Table b

Product	Quantity
a	10
a	20
b	5
b	5

The output that I'm looking for is this:

item	Qty	Product	Quantity
a	10	a	10
a	15	a	20
a	5	NULL	NULL
b	10	b	5
NULL	NULL	b	5

Answer 1

You will need to have some sort of order to guarantee consistent results. To simulate that, I added IDENTITY columns

Match Product to Item in Order Based on ROW_NUMBER()

DROP TABLE IF EXISTS #Table1
DROP TABLE IF EXISTS #Table2

CREATE TABLE #Table1 (ID INT IDENTITY(1,1),Item CHAR(1),Qty INT)
CREATE TABLE #Table2 (ID INT IDENTITY(1,1),Product CHAR(1),Qty INT)
INSERT INTO #Table1
VALUES ('a',10)
,('a',15)
,('a',5)
,('b',10)

INSERT INTO #Table2
VALUES ('a',10)
,('a',20)
,('b',5)
,('b',5)


;WITH cte_Table1 AS (
    SELECT *,RankNum = ROW_NUMBER() OVER (PARTITION BY Item ORDER BY ID)
    FROM #Table1
),
cte_Table2 AS (
    SELECT *,RankNum = ROW_NUMBER() OVER (PARTITION BY Product ORDER BY ID)
    FROM #Table2
)
SELECT *
FROM cte_Table1 AS A
FULL JOIN cte_Table2 AS B
    ON A.Item = B.Product
    AND A.RankNum = B.RankNum