Subselect and Max - tsql

Question

Alright, I've been trying to conceptualize this for a better part of the afternoon and still cannot figure out how to structure this subselect.
The data that I need to report are ages for a given student major grouped by the past 3 fiscal years. Each fiscal year has 3 semesters (summer, fall, spring). I need to have my query grouped on the fiscalyear and agerange fields and then count the distinct student id's.
I currently have this for my SQL statement:
Select COUNT(distinct StuID), AgeRange, FiscalYear
from tblStatic
where Campus like 'World%' and (enrl_act like 'REG%' or enrl_act like 'SCH%')
and StuMaj = 'LAWSC' and FiscalYear IN ('09/10', '10/11', '11/12')
group by FiscalYear, AgeRange
order by FiscalYear, AgeRange
So this is all fine and dandy except it doesn't match my headcount of students for the fiscalyear. The reason being, that people may cross over in the age ranges during the fiscal year and is adding them to my count twice.
How can I use a subselect to resolve this duplicate entry? The field I have been trying to get working is my semester field and using a max to find the max semester during a fiscalyear for a given student.
Data Sample:
Count AgeRange FiscalYear
3 1 to 19 09/10
20 20 to 23 09/10
60 24 to 29 09/10
96 30 to 39 09/10
34 40 to 49 09/10
14 50 to 59 09/10
3 60+ 09/10
2 1 to 19 10/11
24 20 to 23 10/11
73 24 to 29 10/11
109 30 to 39 10/11
43 40 to 49 10/11
11 50 to 59 10/11
2 60+ 10/11
1 1 to 19 11/12
17 20 to 23 11/12
75 24 to 29 11/12
123 30 to 39 11/12
44 40 to 49 11/12
14 50 to 59 11/12
2 60+ 11/12
Solution: (Just got this working and produced my headcounts that match what they are suppose to be)
Select COUNT(distinct S.StuID), AR.AgeRange, S.FiscalYear
from tblStatic S
INNER JOIN
( Select S.StuID, MIN(AgeRange) as AgeRange
From tblStatic S
Group By S.StuID) AR on S.StuID=AR.StuID
where Campus like 'World%' and (enrl_act like 'REG%' or
enrl_act like 'SCH%')
and StuMaj = 'LAWSC' and FiscalYear IN ('09/10', '10/11', '11/12')
group by S.FiscalYear, AR.AgeRange
order by S.FiscalYear, AR.AgeRange

Answer 1

Replace each student's age range with its maximum (or minimum, if you like) age range that fiscal year, then count them:
;
WITH sourceData AS (
SELECT
StudID,
MaxAgeRangeThisFiscalYear = MAX(AgeRange) OVER
(PARTITION BY StudID, FiscalYear),
FiscalYear
FROM tblStatic
WHERE Campus LIKE 'World%'
AND (enrl_act LIKE 'REG%' OR enrl_act LIKE 'SCH%')
AND StuMaj = 'LAWSC'
AND FiscalYear IN ('09/10', '10/11', '11/12')
)
SELECT
FiscalYear,
AgeRange = MaxAgeRangeThisFiscalYear,
Count = COUNT(DISTINCT StudID)
FROM sourceData
GROUP BY
FiscalYear,
MaxAgeRangeThisFiscalYear
ORDER BY
FiscalYear,
MaxAgeRangeThisFiscalYear