--年龄小于17岁的女学生的学号和姓名
SELECT S#, SNAME
FROM S
WHERE AGE < 17 AND SEX = 'F'
--男学生所学课程的课程号和课程名
SELECT DISTINCT C.C#, CNAME --DISTINCT 为了不重复
FROM C, S, SC
WHERE C.C# = SC.C# AND S.S# = SC.S# AND SEX = 'M'
--男学生所学课程的任课老师的工号和姓名
SELECT DISTINCT T.T#, TNAME
FROM T, C, SC, S
WHERE T.T# = C.T# AND C.C# = SC.C# AND S.S# = SC.S# AND SEX = 'M'
--至少选修两门课程的学生学号
SELECT DISTINCT X.S#
FROM SC AS X, SC AS Y
WHERE X.S# = Y.S# AND X.C# != Y.C#
--至少有学号为S2和S4学生选修的课程的课程号
SELECT X.C#
FROM SC AS X, SC AS Y
WHERE X.C# = Y.C# AND X.S# = 'S2' AND Y.S# = 'S4'
--WANG同学不学的课程的课程号
SELECT C.C#
FROM C
WHERE C.C# NOT IN(SELECT SC.C#
FROM SC, C, S
WHERE SC.C# = C.C# AND SC.S# = S.S# AND SNAME = 'WANG')
--全部学生都选修的课程的课程号与课程名
--(双重否定句:没有一名学生不学的课程)
--(直接双重否定即可,想明白是把什么东西组合并且和SC匹配)
SELECT C#, CNAME
FROM C
WHERE NOT EXISTS(SELECT *
FROM S
WHERE NOT EXISTS(SELECT *
FROM SC
WHERE C.C# = SC.C# AND S.S# = SC.S#))
--选修课程包含LIU老师所授全部课程的学生学号
SELECT S#
FROM S
WHERE NOT EXISTS(SELECT *
FROM C, T
WHERE C.T# = T.T# AND T.TNAME = 'LIU' AND NOT EXISTS(SELECT *
FROM SC
WHERE S.S# = SC.S# AND SC.C# = C.C#))