Data for the person you are looking for is not available, because he/she is no member of the group Weimar.
select titel,vorname, nachname, mailaddr, login, user_nr, mailen, ExtMail, suchbar, webseite, url, Positionen.Position, raum,
BeschreibungHTML, Raum_db.bezeichnung, Raum_db.tel_nummer, Raum_db.fax_nummer, GruppenID, deaktiviert
FROM ((User_db left join Raum_db on (Raum_db.raum_nr=User_db.raum))
left join Positionen on (Positionen.PosID=User_db.position))
where user_nr ="1019" and GruppenID=6 and suchbar in ('y','ex')