1、将所有的课程的名称以及对应的任课老师姓名打印出来，如下：
SELECT cname,tname FROM course INNER JOIN teacher WHERE course.teacher_id=teacher.tid

2、查询学生表中男女生各有多少人？ 如下：
SELECT gender,COUNT(gender) 人数 FROM student GROUP BY gender
3、查询物理成绩等于100的学生的姓名？如下：
SELECT sid,sname FROM student WHERE sid in (SELECT student_id FROM score WHERE course_id=2 and num=100)

4、查询平均成绩大于八十分的同学的姓名和平均成绩，如下：
SELECT sname,平均成绩 from (SELECT sid,sname from student) s INNER JOIN
(SELECT student_id,avg(num) 平均成绩 from score GROUP BY student_id HAVING avg(num)>80) c
WHERE sid=student_id

5、查询所有学生的学号，姓名，选课数，总成绩
SELECT s.sid,s.sname,x.课程数,x.总成绩 FROM (SELECT sid,sname FROM student) s INNER JOIN
(SELECT student_id,COUNT(course_id) 课程数,SUM(num) 总成绩 from score GROUP BY student_id) x
WHERE sid=student_id

6、查询姓李老师的个数
SELECT COUNT(tid) FROM teacher WHERE tname like ‘李%‘

7、查询没有报李平老师课的学生姓名
SELECT DISTINCT sname FROM student WHERE sid not in (SELECT DISTINCT student_id FROM score WHERE course_id in (SELECT cid from course WHERE teacher_id=2))

8、查询物理课程比生物课程高的学生的学号
SELECT sw.student_id from (SELECT student_id,num from score WHERE course_id=2) wl INNER JOIN
( SELECT student_id,num from score WHERE course_id=1) sw
WHERE wl.num>sw.num and wl.student_id=sw.student_id

9、查询没有同时选修物理课程和体育课程的学生姓名
SELECT sname FROM student WHERE sid in
(SELECT wl.student_id FROM (SELECT student_id,course_id from score WHERE course_id=2) wl INNER JOIN
(SELECT student_id,course_id from score WHERE course_id=3) ty
WHERE wl.student_id=ty.student_id)

10、查询挂科超过两门(包括两门)的学生姓名和班级
SELECT sname,caption FROM class INNER JOIN
(SELECT sname,class_id from student INNER JOIN (SELECT student_id,COUNT(student_id) 挂科次数 FROM score
WHERE num<60 GROUP BY student_id) gk WHERE sid=student_id and 挂科次数>=2) s
WHERE cid=class_id

11 、查询选修了所有课程的学生姓名
SELECT sname FROM student WHERE sid in (SELECT c.student_id FROM (SELECT a.student_id FROM (SELECT * from score WHERE course_id=1) a
INNER JOIN (SELECT * from score WHERE course_id=2) b
WHERE a.student_id=b.student_id) c INNER JOIN
(SELECT a.student_id FROM (SELECT * from score WHERE course_id=2) a
INNER JOIN (SELECT * from score WHERE course_id=3) b
WHERE a.student_id=b.student_id) d
WHERE c.student_id=d.student_id)

12、查询李平老师教的课程的所有成绩记录
 SELECT sid,sname,cname,num FROM course INNER JOIN (SELECT student.sid,sname,course_id,num FROM student INNER JOIN (SELECT * FROM score WHERE course_id in
(SELECT cid FROM course WHERE teacher_id=(SELECT tid FROM teacher WHERE tid=2))) a
WHERE student.sid=a.student_id) a WHERE cid=a.course_id

 13、查询全部学生都选修了的课程号和课程名：没有
SELECT * from (SELECT course_id,COUNT(student_id) 报名人数 FROM score GROUP BY course_id) a INNER JOIN
(SELECT COUNT(sid) 学生总数 FROM student) b
WHERE 报名人数=学生总数

-- 14、查询每门课程被选修的次数
SELECT course.cname,a.aa from (select course_id,count(course_id)as aa from score GROUP BY course_id)as a
INNER JOIN course on course.cid=a.course_id

-- 15、查询之选修了一门课程的学生姓名和学号
SELECT student.sid,student.sname,a.aa from (SELECT student_id,count(student_id) as aa from score GROUP BY student_id having aa=1) as a
INNER JOIN student on student.sid=a.student_id

-- 16、查询所有学生考出的成绩并按从高到低排序（成绩去重）
select DISTINCT(num) FROM score ORDER BY num DESC

-- 17、查询平均成绩大于85的学生姓名和平均成绩
SELECT student.sname,a.aa from (SELECT student_id,avg(num) as aa from score GROUP BY student_id having aa >85) as a
INNER JOIN student on student.sid=a.student_id

-- 18、查询生物成绩不及格的学生姓名和对应生物分数
select student.sname,a.num from (SELECT * from score where num < 60 and course_id=
(SELECT cid FROM course where cname=‘生物‘)) as a
 INNER JOIN student on student.sid=a.student_id