Measure for Unique Records from Previous Term

[MarkSmash]

Hello,

I'm looking to get a measure, "Unique Students Last Year," which would be the number of unique records from the previous term (in this case a term is a school year). The scores are based on the school year, and aren't tied to a specific date for regular time intelligence functions.

End result wanted in a table:

School Year Name	Unique Students	Unique Students Last Year
2020-21	4
2021-22	2	4
2022-23	1	2

Simplified model:

Sample Data:

SchoolYear table:

SchoolYearKey	School Year Name	Order
1	2020-21	-2
2	2021-22	-1
3	2022-23	0

TestScores table:

ScoreKey	Score	Student	Subject	SchoolYearKey
1	10	1001	Math	1
5	15	1001	Math	2
4	16	1004	Math	1
3	17	1003	Math	1
8	18	1001	English	1
2	20	1002	Math	1
6	20	1002	Math	2
7	20	1001	Math	3
9	20	1001	English	2

Thanks!

[speedramps]

Thank you for the kudos.
If you need more help then raise a new ticket and quote @speedramps anywhere in the text,  I will then receive an automatic notification and will be delighted to help you again.
Please always try provide example input data as table text (not a screen print) so we can import the data to build a solution for you. You will gain respect and a much quicker and better responses with the more effort put in to describing problems  

[speedramps · Accepted solution]

Click here to download the solution
Download PBIX 

How iit works ...

Students this year = 
DISTINCTCOUNT(TestScores[Student])

Students previous year = 
VAR thisref= SELECTEDVALUE(SchoolYear[Order])
VAR previousref= thisref - 1
RETURN
CALCULATE(
DISTINCTCOUNT(TestScores[Student]),
ALL(SchoolYear),
SchoolYear[Order] = previousref)

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If you need more help then please raise a new ticket and quote @speedramps 
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[MarkSmash]

Ahh--All(SchoolYear) was the missing piece for me. Thanks for the quick response!