Calculate Average of each month in SQL Server - sql

Question

I'm having two tables
Promo
ID | Name
---+---------
1 Front
2 Middle
3 Back
PromoRate
ID | Date | Rate | PromoID
---+------------+------+----------
1 2020-01-01 100 1
2 2020-01-02 200 1
3 2020-02-03 300 1
4 2020-02-01 150 2
5 2020-01-02 250 2
6 2020-03-03 350 2
7 2020-03-01 200 3
8 2020-01-02 400 3
9 2020-01-03 600 3
I want to calculate average. Something like this
Name | Avg(Jan) | Avg(Feb) | Avg(Mar)
-------+----------+----------+----------
Front 150 300 NULL
Middle 250 150 350
Back 500 NULL 200
Like pivot or something.
Please help me. Thanks in advance
What I've tried:
SELECT * FROM
(
SELECT P.ID, P.Name, AVG(Rate) AS 'AVG' FROM PromoRate PR
INNER JOIN Promo P ON P.ID = PR.ProfileID
WHERE MONTH(Date) = MONTH(GETDATE())
GROUP BY P.Name, P.ID
) M1
LEFT JOIN
(
SELECT P.ID, P.Name, AVG(Rate) AS 'AVG' FROM PromoRate PR
INNER JOIN Promo P ON P.ID = PR.ProfileID
WHERE MONTH(Date) = MONTH(GETDATE()) + 1
GROUP BY P.Name, P.ID
) M2 ON M1.ID = M2.ID
LEFT JOIN
(
SELECT P.ID, P.Name, AVG(Rate) AS 'AVG' FROM PromoRate PR
INNER JOIN Promo P ON P.ID = PR.ProfileID
WHERE MONTH(Date) = MONTH(GETDATE()) + 2
GROUP BY P.Name, P.ID
) M3 ON M2.ID = M3.ID
But it's not working as expected

Answer 1

You need to group on Month(Date), I'd also use DateAdd rather than month(GetDate()) + 2. You can then use the one query rather than joining on 3 queries as you're going to run into trouble when you cross the year line, or if you have multiple years. E.g. running it in November will also return the results for January that year and next year.
If this is part of a stored procedure I'd also recommend creating an #startdate and #enddate variable and setting those up first.
declare #start datetime
declare #end datetime
select #start = convert(date,GETDATE()), #end = convert(date, DATEADD(month, 2, GETDATE()))
SELECT P.ID, P.Name, AVG(Rate) AS 'AVG' FROM PromoRate PR
INNER JOIN Promo P ON P.ID = PR.ProfileID
WHERE Convert(date, Date) > #start and convert(date, date) < #end
GROUP BY P.Name, P.ID, MONTH(Date)
ETA: You also need to return your month so that you can populate your pivot table.