SELECT Patienten . * , GROUP_CONCAT( IF( CerebrovaskulaereEreignisse.PatNr = Patienten.PatNr, CerebrovaskulaereEreignisse.MTA, NULL ) ) AS 'MTA', GROUP_CONCAT( IF( CerebrovaskulaereEreignisse.PatNr = Patienten.PatNr, CerebrovaskulaereEreignisse.EventDate, NULL ) ) AS 'EventDate'
FROM Patienten
JOIN CerebrovaskulaereEreignisse ON Patienten.PatNr = CerebrovaskulaereEreignisse.PatNr
GROUP BY Patienten.PatNr
LIMIT 0 , 30

results in:
PatNr   BirthDate   Begin       Status  Sex     MTA         EventDate
1   1940-04-29  2001-09-10  1   2   [BLOB - 1B] 2003-09-01
4   1948-01-24  2002-01-29  1   2   [BLOB - 7B] 2008-10-21,2008-04-23,2007-03-05,2007-10-31
6   1969-02-02  2001-02-13  1   1   [BLOB - 1B] 2007-06-01