Chapter five: difficult beer database

Queries:

1. All drinkers that go to A BAR that serves BEERS they LIKE.
2. All drinkers that go to BARS that serve A BEER they DON'T LIKE.
3. All drinkers that go ONLY to BARS that serve A BEER they LIKE.
4. All drinkers that ONLY go to BARS that serve NO BEER they LIKE.
5. All drinkers that ONLY go to BARS that serve ONLY BEER they LIKE.

Database:

likes (drinker, beer)
visits (drinker, bar)
serves (bar, beer)

Examples of the tables:

Drinker	Beer		Drinker	Bar		Bar	Beer
Jan	Heineke		Jan	Cheers		Cheers	Duvel
Jan	Grolsch		Jan	California		Cheers	Grolsch
Jan	Amstel		Jaap	California		Cheers	Heineken
Jan	Leffe		Jaap	Rock cafe		Cheers	Amstel
Jan	Duvel		Peter	Cheers		Cheers	Leffe
Jaap	Grolsch		Peter	Rock cafe		California	Grolsch
Jaap	Duvel		Paul	Cheers		California	Leffe
Peter	Koning		Paul	Flamingo		Rock cafe	Heineke
Peter	Duvel		Mary	California		Rock cafe	Duvel
Peter	Heineken		Mary	Flamingo		Rock cafe	Amstel
Peter	Leffe		Sue	Rock cafe		Flamingo	Heineken
Paul	Heineken		Jolande	California		Flamingo	Grolsch
Paul	Duvel		Jolande	Cheers		Flamingo	Amstel
Paul	Grolsch		Susan	Cheers		Old dutch	Koning
Mary	Grolsch		Susan	Old dutch		Old dutch	Heineken
Sue	Amster					Old dutch	Amstel
Sue	Koning					Old dutch	Grolsch
Sue	Duvel
Jolande	Heineken
Jolande	Grolsch
Jolande	Amstel
Susan	Duvel
Susan	Koning