- song INTEGER NOT NULL REFERENCES songs,
- playmode VARCHAR NOT NULL CHECK playmode IN ('single','double'),
- difficulty VARCHAR NOT NULL CHECK difficulty IN ('beginner','standard','difficult','expert','challenge'),
- feetrating INTEGER NOT NULL CHECK (feetrating >= 0 AND feetrating <= 10)
+ song INTEGER NOT NULL REFERENCES songs, -- strictly song+machine
+ playmode VARCHAR NOT NULL CHECK (playmode IN ('single','double')),
+ difficulty VARCHAR NOT NULL CHECK (difficulty IN ('beginner','standard','difficult','expert','challenge')),
+ feetrating INTEGER NOT NULL CHECK (feetrating >= 0 AND feetrating <= 10),