MySQL Max() with group by and multiple tables - mysql

Question

for my studies i need to get a code working. I do have two tables:
Training:
UserID
Date
Uebung
Gewicht
Wiederholungen
Mitglied:
UserID
Name
Vorname
and i need to display the max power which you get if you multiply 'Wiederholungen' with 'Gewicht' from the 'Training' table for EACH User with the date and name.
I know there is a "problem" with max() and group by. But i'm kinda new to MySQL and i was only able to find fixes with one table and also every column already existing. I have to join two tables AND create the power column.
I tried a lot and i think this may be my best chance
select name, vorname, x.power from
(SELECT mitglied.UserID,max( Wiederholungen*Gewicht) as Power
FROM training join mitglied
where Uebung = 'Beinstrecker'
and training.UserID = mitglied.UserID
group by training.UserID) as x
inner join (training, mitglied)
on (training.UserID = mitglied.UserID)
and x.Power = Power;
'''
I get way too many results. I know the last statement is wrong (x.power = power) but i have no clue how to solve it.

Answer 1

This is actually a fairly typical question here, but I am bad a searching for previous answers so....
You "start" in a subquery, finding those max values:
SELECT UserID, Uebung, MAX(Gewicht*Wiederholugen) AS Power
FROM training
WHERE Uebung = 'Beinstrecker'
GROUP BY UserID, Uebung
Then, you join that back to the table it came from to find the date(s) those maxes occurred:
( SELECT UserID, Uebung, MAX(Gewicht*Wiederholugen) AS Power
FROM training
WHERE Uebung = 'Beinstrecker'
GROUP BY UserID, Uebung
) AS maxes
INNER JOIN training AS t
ON maxes.UserID = t.UserID
AND maxes.Uebeng = t.Uebeng
AND maxes.Power = (t.Gewicht*t.Wiederholugen)
Finally, you join to mitglied to get information for the user:
SELECT m.name, m.vorname, maxes.Power
FROM ( SELECT UserID, Uebung, MAX(Gewicht*Wiederholugen) AS Power
FROM training
WHERE Uebung = 'Beinstrecker'
GROUP BY UserID, Uebung
) AS maxes
INNER JOIN training AS t
ON maxes.UserID = t.UserID
AND maxes.Uebeng = t.Uebeng
AND maxes.Power = (t.Gewicht*t.Wiederholugen)
INNER JOIN mitglied AS m ON t.UserID = m.UserID
;
Note: t.Uebung = 'Beinstrecker' could be used as a join condition instead, and might be faster; but as a matter of style I try to prevent redundant literals like that unless there is a worthwhile performance difference.