Get data from two date ranges within same table (MSSQL) - sql-server

Question

I have this query:
SELECT
COUNT(DISTINCT ProdTr.OrdNo) AS Orders,
ProdTr.YrPr AS Period,
SUM(ProdTr.DAm) AS Total,
SUM(ProdTr.IncCst) AS Cost
FROM ProdTr
WHERE ProdTr.TrTp = 1 AND ProdTr.CustNo != 0
AND ProdTr.YrPr BETWEEN (201901) AND (201912)
GROUP BY ProdTr.YrPr
ORDER BY ProdTr.YrPr ASC
And it works well. It yields the expected result, sales data from the date period 2019-01 to 2019-12. Result:
I would like to add an extra column that shows the same data - but from last year. For period 2019-01 it should show sales data for 2018-01 (1 year back). I managed to do this with a subquery, but it is slow - and seems like a bad idea.
Are there any better ways to achieve this? Database version is MSSQL 2016.
Thank you very much for your time.

Answer 1

You can do it with conditional aggregation:
SELECT
COUNT(DISTINCT CASE WHEN LEFT(YrPr, 4) = '2019' THEN OrdNo END) AS Orders2019,
'2019' + RIGHT(YrPr, 2) AS Period2019,
SUM(CASE WHEN LEFT(YrPr, 4) = '2019' THEN DAm END) AS Total2019,
SUM(CASE WHEN LEFT(YrPr, 4) = '2019' THEN IncCst END) AS Cost2019,
SUM(CASE WHEN LEFT(YrPr, 4) = '2018' THEN DAm END) AS Total2018
FROM ProdTr
WHERE TrTp = 1 AND CustNo != 0
AND YrPr BETWEEN (201801) AND (201912)
GROUP BY RIGHT(YrPr, 2)
ORDER BY Period2019 ASC

Answer 2

You could do it like this:
WITH TwoYears AS (
SELECT COUNT(DISTINCT ProdTr.OrdNo) AS Orders
, ProdTr.YrPr AS Period
, SUM(ProdTr.DAm) AS Total
, SUM(ProdTr.IncCst) AS Cost
FROM ProdTr
WHERE ProdTr.TrTp = 1
AND ProdTr.CustNo != 0
AND ProdTr.YrPr BETWEEN 201801 AND 201912
GROUP BY ProdTr.YrPr
), CurrentYear AS (
SELECT Orders, Period, Total, Cost
FROM TwoYears
WHERE Period >= 201901
), PreviousYear AS (
SELECT Orders, Period, Total, Cost
FROM TwoYears
WHERE Period < 201901
)
SELECT c.Orders, c.Period, c.Total, c.Cost
, p.Orders AS PrevOrders, p.Period AS PrevPeriod, p.Total AS PrevTotal, p.Cost AS PrevCost
FROM CurrentYear c
FULL JOIN PreviousYear p ON p.Period = c.Period - 100
ORDER BY COALESCE(c.Period, p.Period + 100)