SQL Selecting Max Value 4 Joins - sql

Question

I´m stuck with this Query. I want to get the following information from my Database:
User.username, Satz.Gewicht, Satz.Wiederholungen, ubungen.Name and Training.Datum
The Clue is, that I want to get this Columns for every different Exercise (ubungen.id).
I Tried with this:
SELECT
a3.Datum,
a4.username,
a2.Name,
max(Gewicht) as Gewicht,
Wiederholungen
from satz a1
INNER JOIN ubungen a2 ON a1.UBID = a2.ID
INNER JOIN training a3 ON a1.TID = a3.ID
INNER JOIN user a4 ON a3.UID = a4.ID
GROUP BY a1.UBID
But Somehow I´m getting the right Weight -> max(Gewicht) , but the wrong user.
What am I doing wrong?
Here is a Screenshot of my database design:
EDIT:
When using every column in my Group by I get Multiple Columns like this:
But i Just want the one in the middle at it is the one with the highest Gewicht.
Example of what I want:
This is the whole resultset after Joining the information I want. Now I just want the Lines that are marked in red. There are some lines having the same "max(gewicht)", no matter which of the ones to pick.

Answer 1

You have to use all the columns in the GROUP BY except aggregated function column
Try this out:
SELECT
a3.Datum, a4.username, a2.Name, max(Gewicht) as Gewicht, Wiederholungen
FROM satz a1
INNER JOIN ubungen a2
ON a1.UBID = a2.ID
INNER JOIN training a3
ON a1.TID = a3.ID
INNER JOIN user a4
ON a3.UID = a4.ID
GROUP BY
a3.Datum, a4.username, a2.Name, Wiederholungen

Answer 2

I think you are just looking for the record with the maximum value for each ubid:
select x.Ubid,x.Datum,x.username,x.name,x.Gewicht,x.Wiederholungen
from
(SELECT
a1.Ubid,
a3.Datum,
a4.username,
a2.Name,
Gewicht,
Wiederholungen,
row_number() over (partition by a1.ubid order by Gewicht desc) as rownum1
from satz a1
INNER JOIN ubungen a2 ON a1.UBID = a2.ID
INNER JOIN training a3 ON a1.TID = a3.ID
INNER JOIN user a4 ON a3.UID = a4.ID ) x
where x.rownum1=1
I have made use of the row_number function to pull the record with the highest Gewicht value. Hope this helps.
Edit: Adding a db-fiddle, it's working fine in this example:
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=0ac9caf422a06feb6e7c05c1a68995f5
Since row_number is not working, you can use an inner join to get the max value:
select x.Ubid,x.Datum,x.name,x.Gewicht,max(x.Wiederholungen) as Wiederholungen,max(x.username) as username
from
(SELECT
a1.Ubid,
a3.Datum,
a4.username,
a2.Name,
a1.Gewicht,
a1.Wiederholungen
from satz a1
INNER JOIN ubungen a2 ON a1.UBID = a2.ID
INNER JOIN training a3 ON a1.TID = a3.ID
INNER JOIN user a4 ON a3.UID = a4.ID ) x
INNER JOIN
(select ubid,max(Gewicht) as max_Gewicht from satz group by ubid) y
ON x.ubid=y.ubid and x.Gewicht=y.max_Gewicht
Group by x.Ubid,x.Datum,x.name,x.Gewicht

Answer 3

Your query runs, but it's malformed.
Columns not specified in the GROUP BY clause should be aggregated. MariaDB (and MySQL) are notorious by allowing non-aggregated columns in the SELECT clause.
Solution: Just add all non-aggregated columns to the GROUP BY clause to solve your issue, as in:
GROUP BY a1.UBID, a3.Datum, a4.username, a2.Name, Wiederholungen
As it is, MariaDB is selecting values randomly. Today you see the wrong values, but maybe tomorrow they are good. You don't want a query behaving like this.