Division in SQL

• Let’s do it the hard way, without EXCEPT:

SELECT S.sname

FROM Sailors S

WHERE NOT EXISTS

((SELECT B.bid

FROM Boats B)

EXCEPT

(SELECT R.bid

FROM Reserves R

WHERE R.sid=S.sid))

SELECT S.sname

FROM Sailors S

WHERE NOT EXISTS (SELECT B.bid

FROM Boats B

WHERE NOT EXISTS (SELECT R.bid

FROM Reserves R

WHERE R.bid=B.bid

AND R.sid=S.sid))

Sailors S such that ...

there is no boat B without ...

a Reserves tuple showing S reserved B

Find sailors who’ve reserved all boats.

(1)

(2)

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