How to get max value and corresponding date in SQL Server

Question

I have a table of locations, dates, and altitude values. The query below is easy, but I'm trying to get min/max dates that correspond to the min/max values of altitude.

SELECT location, 
max(datetime) as max_date
COUNT(Altitude) as COUNT, 
AVG(Altitude) as AVG,
MIN(Altitude) as MIN,
max(Altitude) as MAX
FROM mydatabase
GROUP BY location

Answer 1

For every location select max and min altitude and max min datetime for them.

    select location, Altitude, min([datetime]) dtmin, max([datetime]) dtmax
    from (
       SELECT location, Altitude, [datetime]
           , min(Altitude) over(partition by location) as aMIN
           , max(Altitude) over(partition by location) as aMAX
       FROM mydatabase
    ) t
    where Altitude in (aMIN, aMAX)
    group by location, Altitude
    order by location, Altitude;