7、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分；
SELECT course.cid a,MIN(score.`num`) d,MAX(score.`num`) c FROM course INNER JOIN score ON course.cid=score.course_id GROUP BY course.cname;
8、查询课程编号“2”的成绩比课程编号“1”课程低的所有同学的学号、姓名；
SELECT s.sid,s.sname FROM student s WHERE
(
(SELECT score.num FROM score WHERE s.sid=score.student_id AND score.course_id='2')
<(SELECT score.num FROM score WHERE s.sid=score.student_id AND score.course_id='1')
)
9、查询“生物”课程比“物理”课程成绩高的所有学生的学号；
10、查询平均成绩大于60分的同学的学号和平均成绩;
SELECT student_id,AVG(num) FROM score GROUP BY student_id HAVING AVG(num) >60;
11、查询所有同学的学号、姓名、选课数、总成绩；
SELECT s.sid,COUNT(c.cid),s.sname,SUM(sc.num) FROM student s INNER JOIN score sc ON
s.sid = sc.student_id INNER JOIN course c ON s.sid =c.cid GROUP BY c.cname;
12、查询姓“李”的老师的个数；
SELECT COUNT(tid) FROM teacher WHERE tname LIKE '李%'
13、查询没学过“张磊老师”课的同学的学号、姓名；
SELECT sid,sname FROM student WHERE class_id NOT IN(
SELECT teacher.`tid` FROM student,teacher WHERE teacher.`tname`='张磊老师' AND teacher.`tid`=student.`class_id`
)
14、查询学过“1”并且也学过编号“2”课程的同学的学号、姓名；
SELECT sname,sid FROM student WHERE sid IN(SELECT student_id FROM score WHERE course_id IN(1,2));
15、查询学过“李平老师”所教的所有课的同学的学号、姓名；
SELECT sid,sname FROM student WHERE class_id IN(
SELECT teacher.`tid` FROM student,teacher WHERE teacher.`tname`='李平老师' AND teacher.`tid`=student.`class_id`
)