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3.查询平均成绩大于60分的同学的学号和平均成绩；姓名
SELECT student.s_id,a,student.s_name FROM
(select s_id,avg(s_score)as a from score GROUP BY s_id having avg(s_score)>60) as y
LEFT JOIN student on y.s_id=student.s_id
5.查询姓“李”的老师的个数；
SELECT * FROM teacher WHERE t_name LIKE '李%'
7.查询学过“001”并且也学过编号“002”课程的同学的学号、姓名；
SELECT b.s_id,s_name FROM (SELECT a.s_id FROM
(SELECT s_id,c_id FROM score WHERE c_id=01 or c_id=02) as a
GROUP BY a.s_id
HAVING count(a.s_id)>1) as b
left outer join student on student.s_id=b.s_id
8.查询学过“叶平”老师所教的所有课的同学的学号、姓名；
SELECT a.s_id,s_name FROM
(SELECT s_id from score WHERE c_id in
(SELECT c_id FROM course LEFT JOIN teacher on teacher.t_id=course.t_id WHERE t_name="李四"))as a
left outer join student on a.s_id=student.s_id
10.查询有课程成绩小于60分的同学的学号、姓名；
select a.s_id,s_name from (select s_id FROM score WHERE s_score<60 GROUP BY s_id) as a
left outer join student on student.s_id=a.s_id
11.查询没有学全所有课的同学的学号、姓名；
SELECT a.s_id,s_name FROM
(select s_id FROM score GROUP BY s_id HAVING count(c_id)<(select count(c_id) FROM course)) as a
left outer join student
on student.s_id = a.s_id
12.查询至少有一门课与学号为“001”的同学所学相同的同学的学号和姓名；
SELECT a.s_id,s_name FROM(select s_id FROM score WHERE s_id !=1 and c_id in (SELECT c_id FROM score WHERE s_id=01 ) GROUP BY s_id) as a
left outer join student on a.s_id=student.s_id
13、查询至少学过学号为“001”同学所选课程中任意一门课的其他同学学号和姓名；
这题目不是跟上面的一模一样吗？？？
SELECT a.s_id,s_name FROM(select s_id FROM score WHERE s_id !=1 and c_id in (SELECT c_id FROM score WHERE s_id=01 ) GROUP BY s_id) as a
left outer join student on a.s_id=student.s_id
14.查询和“002”号的同学学习的课程完全相同的其他同学学号和姓名；（跳过）
select score.s_id,s_name from score
left join student on score.s_id = student.s_id
where s_id in
(select s_id from score where s_id != 02
group by s_id
HAVING count(c_id) = (select count(1) from score where s_id = 02))
and
c_id in (select c_id from score where s_id = 1)
group by s_id
HAVING count(c_id) = (select count(c_id) from score where s_id = 02) #跟02一样课程选择数的学号
15、删除学习“李四”老师课的score表记录；
DELETE from score WHERE c_id= (select c_id from course WHERE t_id=(SELECT t_id FROM teacher where t_name LIKE("李四")))
16.向SC表中插入一些记录，这些记录要求符合以下条件：需要注意：从另一张表导入的学号
①没有上过编号“002”课程的同学学号；②插入“002”号课程的平均成绩；
insert into score(s_id,c_id,s_score)
select
s_id,2,(SELECT avg(s_score) from score WHERE c_id=02)
FROM
student WHERE s_id NOT in (SELECT s_id from score WHERE c_id=02 GROUP BY s_id)
17、按平均成绩从低到高显示所有学生的“语文”、“数学”、“英语”三门的课程成绩，按如下形式显示： 学生ID,语文,数学,英语,有效课程数,有效平均分；
SELECT
s_id as'学生ID',
(SELECT s_score FROM score as a where c_id=01 and a.s_id=score.s_id LIMIT 0,1) as '语文',
(SELECT s_score FROM score as a where c_id=02 and a.s_id=score.s_id LIMIT 0,1) as '数学',
(SELECT s_score FROM score as a where c_id=03 and a.s_id=score.s_id LIMIT 0,1) as '英语',
count(c_id) as '有效课程数',
avg(s_score) as '平均分'
FROM score
GROUP BY s_id
ORDER BY '平均分' asc
18、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 c_id,max(s_score),min(s_score) from score
GROUP BY c_id
19、按各科平均成绩从低到高和及格率的百分数从高到低顺序；（排序不管用）试了+0 *1 CAST CONVERT 都不管用
select
c_id as '课程ID',
AVG(s_score)as '平均分',
(sum(case when score.s_score>60 then 1 else 0 end)/count(1)*100)+0 as '及格率(%)'
from score
GROUP BY c_id
order by '及格率(%)'
20、课程平均分从高到低显示（显示任课老师）；
SELECT t_name,b from
(select c_id,AVG(s_score) as b from score GROUP BY c_id )as a
LEFT JOIN course on a.c_id=course.c_id
LEFT JOIN teacher on course.t_id=teacher.t_id
ORDER BY b desc
21.查询各科成绩前三名的记录:(不考虑成绩并列情况)
SELECT * FROM
(select * from score where c_id=01 order by s_score desc limit 0,3)as a,
(select * from score where c_id=02 order by s_score desc limit 0,3)as b,
(select * from score where c_id=03 order by s_score desc limit 0,3)as c,
(select * from score where c_id=04 order by s_score desc limit 0,3)as d,
(select * from score where c_id=05 order by s_score desc limit 0,3)as e,
(select * from score where c_id=06 order by s_score desc limit 0,3)as f,
(select * from score where c_id=07 order by s_score desc limit 0,3)as g
where a.s_id=b.s_id=c.s_id=d.s_id=e.s_id=f.s_id=g.s_id
22.查询每门课程被选修的学生数；
select c_id,count(s_id) from score GROUP BY c_id
23.查询出只选修了一门课程的全部学生的学号和姓名；
select s_id from score
GROUP BY s_id
HAVING COUNT(c_id)=1
24、查询男生、女生的人数；
select *,(SELECT count(s_id) from student where s_sex ='女')as '女人数' from (SELECT count(s_id)as '男人数' from student where s_sex ='男')as a