Mysql 综合练习
1、查询男生、女生的人数；
mysql> select gender, count(sid) from student group by gender;
2、查询姓“张”的学生名单；
3、课程平均分从高到低显示
mysql> select course_id, cname,avg_num from course inner join
(select course_id,avg(num) as avg_num from score group by course_id) as t1
where cid=t1.course_id
group by avg_num desc;
4、查询有课程成绩小于60分的同学的学号、姓名；
mysql> select sname, sid from student where sid in (select distinct student_id from score where num < 60);
5、查询至少有一门课与学号为1的同学所学课程相同的同学的学号和姓名；
select sid,sname from student where sid in
(select distinct student_id from score where course_id in
(select course_id from score where student_id = 1)) ;
6、查询出只选修了一门课程的全部学生的学号和姓名；
select * from student inner join (select student_id, count(course_id) from score group by student_id having count(course_id)=1) as bb on sid = bb.student_id ;
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_id, max(num),min(num) from score group by course_id ;
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；
# 先找到每个学生的课程编号“1”的和课程编号“2”的成绩组成一张表
select t1.student_id from(select num num2,student_id from score where course_id = 2) t2 inner join(select student_id,num num1 from score where course_id = 1) t1 on t1.student_id = t2.student_id
# 再找到课程编号“2”的成绩比课程编号“1”课程低的所有学生的学号
select t1.student_id from(select num num2,student_id from score where course_id = 2) t2 inner join(select student_id,num num1 from score where course_id = 1) t1 on t1.student_id = t2.student_id where num2 < num1
# 再找到所有学生的学号、姓名
select sid,sname from student where sid in(select t1.student_id from(select num num2,student_id from score where course_id = 2) t2 inner join(select student_id,num num1 from score where course_id = 1) t1 on t1.student_id = t2.student_id where num2 < num1);
9、查询“生物”课程比“物理”课程成绩高的所有学生的学号；
select student_id,shengwu_score,wuli_score from (
(select student_id, num as shengwu_score from score where course_id in
(select cid from course where cname="生物")) as t1
inner join
(select student_id as student_id2, num as wuli_score from score where course_id in
(select cid from course where cname="物理")) as t2
on t1.student_id = t2.student_id2)
where shengwu_score > wuli_score;
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 student_id,sname, sum(num), count(course_id) from score
inner join student on student.sid = student_id group by student_id;
12、查询姓“李”的老师的个数；
select count(tid ) as li_ciunter from ( select * from teacher where tname like "李%") as teacher;
13、查询没学过“张磊老师”课的同学的学号、姓名；
select distinct sname, student_id from student inner join score on student.sid =student_id where
course_id not in
(select tid from teacher where tname like "张磊老师");
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 t1.1_id from
(select student_id as 1_id from score where course_id = 1 ) t1
inner join
(select student_id as 2_id from score where course_id = 2)t2
on t1.1_id = t2.2_id);
15、查询学过“李平老师”所教的所有课的同学的学号、姓名；
select * from student where sid in (
select distinct student_id from score where course_id in
(select cid from course where teacher_id = (
select tid from teacher where tname = "李平老师")));