Du kunne bruge en hanving for count distinkt drinkgruppe af DRINKER
SELECT DRINKERS.DRINKER
FROM DRINKERS
INNER JOIN ORDERS DRINKERS.DRINKER = ORDERS.DRINKER
WHERE ORDERS.DRINK IN ( 'VODKA' , 'WHISKY')
GROUP BY DRINKER
HAVING COUNT(DISTINCT ORDERS.DRINK ) = 2
eller hvis du har brug for en indlejret
SELECT DISTINCT DRINKER
FROM DRINKERS
WHERE EXISTS (SELECT DRINKER
FROM ORDERS
WHERE DRINK IN ( 'VODKA' AND 'WHISKY')
GROUP BY DRINKER
HAVING COUNT(DISTINCT ORDERS.DRINK ) = 2
);