Find sid’s of sailors who’ve reserved a red or a green boat

• UNION: Can be used to compute the union of any two union-compatible sets of tuples (which are themselves the result of SQL queries).

• If we replace OR by AND in the first version, what do we get?

• Also available: EXCEPT (What do we get if we replace UNION by EXCEPT?)

SELECT S.sid

FROM Sailors S, Boats B, Reserves R

WHERE S.sid=R.sid AND R.bid=B.bid

AND (B.color=‘red’ OR B.color=‘green’)

SELECT S.sid

FROM Sailors S, Boats B, Reserves R

WHERE S.sid=R.sid AND R.bid=B.bid

AND B.color=‘red’

UNION

SELECT S.sid

FROM Sailors S, Boats B, Reserves R

WHERE S.sid=R.sid AND R.bid=B.bid

AND B.color=‘green’

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