SELECT *
FROM mitarbeiter m
join
(SELECT mnr as x, count(thema) as ANZAHL FROM
(SELECT k.mnr, b.thema FROM
kundenbetreuer k right
join betreut b on
(k.mnr = b.betreuer)
GROUP BY k.mnr, b.thema)
GROUP BY mnr HAVING anzahl =
(SELECT max(t) FROM (SELECT count(thema) as t from betreut group by betreuer, thema))
on (m.mnr = x)
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