Distinct count for entire dataset, grouped by month - sql

Question

I am dealing with a sales order table (ORDER) that looks roughly like this (updated 2018/12/20 to be closer to my actual data set):
SOID SOLINEID INVOICEDATE SALESAMOUNT AC
5 1 2018-11-30 100.00 01
5 2 2018-12-05 50.00 02
4 1 2018-12-12 25.00 17
3 1 2017-12-31 75.00 03
3 2 2018-01-03 25.00 05
2 1 2017-11-25 100.00 17
2 2 2017-11-27 35.00 03
1 1 2017-11-20 15.00 08
1 2 2018-03-15 30.00 17
1 3 2018-04-03 200.00 05
I'm able to calculate the average sales by SOID and SOLINEID:
SELECT SUM(SALESAMOUNT) / COUNT(DISTINCT SOID) AS 'Total Sales per Order ($)',
SUM(SALESAMOUNT) / COUNT(SOLINEID) AS 'Total Sales per Line ($)'
FROM ORDER
This seems to provide a perfectly good answer, but I was then given an additional constraint, that this count be done by year and month. I thought I could simply add
GROUP BY YEAR(INVOICEDATE), MONTH(MONTH)
But this aggregates the SOID and then performs the COUNT(DISTINCT SOID). This becomes a problem with SOIDs that appears across multiple months, which is fairly common since we invoice upon shipment.
I want to get something like this:
Year Month Total Sales Per Order Total Sales Per Line
2018 11 0.00
The sore thumb sticking out is that I need some way of defining in which month and year an SOID will be aggregated if it spans across multiple ones; for that purpose, I'd use MAX(INVOICEDATE).
From there, however, I'm just not sure how to tackle this. WITH? A subquery? Something else? I would appreciate any help, even if it's just pointing in the right direction.

Answer 1

You should select Year() and month() for invocedate and group by
SELECT YEAR(INVOICEDATE) year
, MONTH(INVOICEDATE) month
, SUM(SALESAMOUNT) / COUNT(DISTINCT SOID) AS 'Total Sales per Order ($)'
, SUM(SALESAMOUNT) / COUNT(SOLINEID) AS 'Total Sales per Line ($)'
FROM ORDER
GROUP BY YEAR(INVOICEDATE), MONTH(INVOICEDATE)

Answer 2

Here are the results, but the data sample does not have enuf rows to show Months...
SELECT
mDateYYYY,
mDateMM,
SUM(SALESAMOUNT) / COUNT(DISTINCT t1.SOID) AS 'Total Sales per Order ($)',
SUM(SALESAMOUNT) / COUNT(SOLINEID) AS 'Total Sales per Line ($)'
FROM DCORDER as t1
left join
(Select
SOID
,Year(max(INVOICEDATE)) as mDateYYYY
,Month(max(INVOICEDATE)) as mDateMM
From DCOrder
Group By SOID
) as t2
On t1.SOID = t2.SOID
Group by mDateYYYY, mDateMM
mDateYYYY mDateMM Total Sales per Order ($) Total Sales per Line ($)
2018 12 87.50 58.33
I have used new SQL still MAX(INVOICEDATE)(not above), with new 12/20 data, and excluded AC=17.
YYYY MM Total Sales per Order ($) Total Sales per Line ($)
2017 11 35.00 35.00
2018 1 100.00 50.00
2018 4 215.00 107.50
2018 12 150.00 75.00