SQL - Select max week from a group - tsql

Question

I need to be able to get a result set which shows the last teacher for a course, for which I have the following SQL query:
SELECT
a.acad_period, MAX(a.start_week) as start_week,
a.staff_code, b.aos_code, b.aos_period
FROM
qlsdat.dbo.sttstaff a
INNER JOIN
qlsdat..sttrgaos b ON a.acad_period = b.acad_period
AND a.register_id = b.register_id
AND a.register_group = b.register_group
WHERE
a.acad_period = '14/15'
GROUP BY
a.acad_period, a.staff_code, b.aos_code, b.aos_period
However, the issue is that it returns to me the maximum start week for a teacher on that course, whereas I want the maximum start week for a course, and the teacher that happens to be teaching for that start week.
Here is a sample result set returned from the above query:
14/15 37 HKARUNATHIL A2ES 001A
14/15 37 CSHUKLA A2ES 001B
14/15 37 PSEDOV A2ES 002A
14/15 37 BBANFIELD A2ES 002B
14/15 14 VKRISHNASWA A2EX BL1 X
14/15 14 VKRISHNASWA A2EX BL2 X
14/15 6 BODAMEKENTO ACA2 BL1 A
14/15 41 SKLER ACA2 BL1 A
14/15 44 BODAMEKENTO ACAS BL1 F
14/15 37 MMILLER ARA2 BL1 C
14/15 45 MMILLER ARAS BL1 E
14/15 44 SHOULTON ARAS BL1 E
Here is an example of the problem within the result set:
14/15 10 HMALIK MMGX GB2F3
14/15 44 JMULLANEY MMGX GB2F3
In the above example I only want:
14/15 44 JMULLANEY MMGX GB2F3
The query produced is going to be used as a subquery in another query.

Answer 1

This will get the row for highest start_week, however you may encounter some problems if you have data from more than 1 year, this can be resolved by putting your your field in addition to your week column in this part
row_number() over (partition by
a.acad_period, b.aos_code, b.aos_period
order by
a.start_year desc,
a.start_date desc) rn
Query:
;WITH CTE AS
(
SELECT
a.acad_period, a.start_week,
a.staff_code, b.aos_code, b.aos_period,
row_number() over (partition by
a.acad_period, b.aos_code,
b.aos_period
order by a.start_week desc) rn
FROM
qlsdat.dbo.sttstaff a
INNER JOIN
qlsdat..sttrgaos b ON a.acad_period = b.acad_period
AND a.register_id = b.register_id
AND a.register_group = b.register_group
WHERE
a.acad_period = '14/15'
)
SELECT
acad_period, start_week,
staff_code, aos_code, aos_period,
FROM CTE
WHERE rn = 1