- FOREIGN KEY (song, playmode, difficulty) REFERENCES songs (song, playmode, difficulty),
- FOREIGN KEY (tournament, round, parallel) REFERENCES groups (tournament, round, parallel),
- PRIMARY KEY (tournament, round, parallel, player, songs)
-);
+ FOREIGN KEY (song) REFERENCES songs (song),
+ FOREIGN KEY (song, playmode, difficulty) REFERENCES songratings (song, playmode, difficulty),
+ FOREIGN KEY (tournament, round, parallel, player) REFERENCES roundparticipation (tournament, round, parallel, player),
+ PRIMARY KEY (tournament, round, parallel, player, song)
+);