Try something like this. All field and table names are made up, obviously.
Code:
SELECT
T1.MyDate,
T1.MyCell,
First(T1.MyHour),
First(T1.MyAttempts)
FROM
MyTable AS T1,
(SELECT T2.MyDate, T2.MyCell, Max(T2.MyAttempts) AS MaxAttempts
FROM MyTable AS T2
GROUP BY T2.MyDate, T2.MyCell)
WHERE
(T1.MyDate = T2.MyDate
AND T1.MyCell = T2.MyCell
AND T1.MyAttempts = MaxAttempts)
GROUP BY T1.MyDate, T1.MyCell;
I used First(MyHour) because it's likely that multiple hours will have the same number of attempts. If you want to retain the duplicates, then use something like this:
Code:
SELECT
T1.MyDate,
T1.MyCell,
T1.MyHour,
T1.MyAttempts
FROM
MyTable AS T1,
(SELECT T2.MyDate, T2.MyCell, Max(T2.MyAttempts) AS MaxAttempts
FROM MyTable AS T2
GROUP BY T2.MyDate, T2.MyCell)
WHERE
(T1.MyDate = T2.MyDate
AND T1.MyCell = T2.MyCell
AND T1.MyAttempts = MaxAttempts);