SQL Server 2017

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WITH ProductPast AS (
    SELECT 1 AS productID, 10 AS deptID, 2015 AS year, 1 AS month, 45 AS price UNION ALL
    SELECT 1, 10, 2015, 2, 65 UNION ALL
    SELECT 2, 11, 2015, 1, 45 UNION ALL
    SELECT 2, 11, 2015, 2, 65 UNION ALL
    SELECT 2, 11, 2015, 3, 44
),
ProductCurrent AS (
    SELECT 1 AS productID, 10 AS deptID, 2016 AS year, 1 AS month, 12 AS price UNION ALL
    SELECT 1, 10, 2016, 2, 46 UNION ALL
    SELECT 1, 10, 2016, 3, 77 UNION ALL
    SELECT 2, 11, 2016, 1, 88
)

SELECT
    COALESCE(pp.productID, pc.productID) AS productID,
    COALESCE(pp.deptID, pc.deptID) AS deptID,
    COALESCE(pp.month, pc.month) AS Month,
    COALESCE(pp.year, 2015) AS PrevYear,
    COALESCE(pp.price, 0) AS PrevPrice,
    COALESCE(pc.year, 2016) AS CurrYear,        
    COALESCE(pc.price, 0) AS CurrPrice
FROM ProductPast pp
FULL OUTER JOIN ProductCurrent pc
    ON pp.productID = pc.productID AND
       pp.deptID = pc.deptID AND
       pp.year = pc.year - 1 AND
       pp.month = pc.month
ORDER BY
    COALESCE(pp.productID, pc.productID),
    COALESCE(pp.deptID, pc.deptID),
    COALESCE(pp.month, pc.month);

productID	deptID	Month	PrevYear	PrevPrice	CurrYear	CurrPrice
1	10	1	2015	45	2016	12
1	10	2	2015	65	2016	46
1	10	3	2015	0	2016	77
2	11	1	2015	45	2016	88
2	11	2	2015	65	2016	0
2	11	3	2015	44	2016	0