这只是答案的一半…
可以使用条件连接和投影来找到“由两个或多个水手预定的船”的关系，它们都在您允许的操作集中：
SELECt DISTINCT R1.bid FROM Reserves AS R1 JOIN Reserves AS R2 ON R1.bid = R2.bid AND R1.sid < R2.sid;
可以使用条件联接（两次）和投影来找到“三个或三个以上船员预订的船”的关系，它们都在您允许的操作集中：
SELECt DISTINCT R1.bid FROM Reserves AS R1 JOIN Reserves AS R2 ON R1.bid = R2.bid AND R1.sid < R2.sid JOIN Reserves AS R3 ON R1.bid = R3.bid AND R2.sid < R3.sid;
如果 我们
EXCEPT在标准SQL中有减号运算符，例如：
SELECt DISTINCT R1.bid FROM Reserves AS R1 JOIN Reserves AS R2 ON R1.bid = R2.bid AND R1.sid < R2.sidEXCEPTSELECt DISTINCT R1.bid FROM Reserves AS R1 JOIN Reserves AS R2 ON R1.bid = R2.bid AND R1.sid < R2.sid JOIN Reserves AS R3 ON R1.bid = R3.bid AND R2.sid < R3.sid;
如果
我们有限制（
WHERe在SQL中）和半差分（又名antijoin）运算符（例如
NOTIN在SQL中）：
SELECt DISTINCT R1.bid FROM Reserves AS R1 JOIN Reserves AS R2 ON R1.bid = R2.bid AND R1.sid < R2.sid WHERe R1.bid NOT IN (SELECt DISTINCT R1.bid FROM Reserves AS R1 JOIN Reserves AS R2 ON R1.bid = R2.bid AND R1.sid < R2.sid JOIN Reserves AS R3 ON R1.bid = R3.bid AND R2.sid < R3.sid );
…但是您允许的操作集不包括限制，半差或减:(
