一、表关系
请创建如下表，并创建相关约束
| 班级表：class | 学生表：student | ||||||
| cid | caption | grade_id | sid | sname | gender | class_id | |
| 1 | 一年一班 | 1 | 1 | 乔丹 | 女 | 1 | |
| 2 | 二年一班 | 2 | 2 | 艾弗森 | 女 | 1 | |
| 3 | 三年二班 | 3 | 3 | 科比 | 男 | 2 | |
| 老师表：teacher | 课程表：course | ||||||
| tid | tname | cid | cname | teacher_id | |||
| 1 | 张三 | 1 | 生物 | 1 | |||
| 2 | 李四 | 2 | 体育 | 1 | |||
| 3 | 王五 | 3 | 物理 | 2 | |||
| 成绩表：score | 年级表：class_grade | ||||||
| sid | student_id | course_id | score | gid | gname | ||
| 1 | 1 | 1 | 60 | 1 | 一年级 | ||
| 2 | 1 | 2 | 59 | 2 | 二年级 | ||
| 3 | 2 | 2 | 99 | 3 | 三年级 | ||
| 班级任职表：teach2cls | |||||||
| tcid | tid | cid | |||||
| 1 | 1 | 1 | |||||
| 2 | 1 | 2 | |||||
| 3 | 2 | 1 | |||||
| 4 | 3 | 2 |
二、操作表
-- 1、自行创建测试数据； create database db5; use db5; create table teacher ( tid int primary key auto_increment, tname char(20) not null ); insert into teacher(tname) values ('张三'), ('李四'), ('王五'), ('赵六'), ('马七'); create table class_grade ( gid int primary key auto_increment, gname char(20) not null ); insert into class_grade(gname) values ('一年级'), ('二年级'), ('三年级'), ('四年级'), ('五年级'); create table course ( cid int primary key auto_increment, cname char(20) not null, teacher_id int, foreign key(teacher_id) references teacher(tid) on delete cascade on update cascade ); insert into course(cname, teacher_id) values ('生物',1), ('体育',1), ('物理',2), ('语文',3), ('数学',4), ('外语',5); create table class ( cid int primary key auto_increment, caption char(20), grade_id int, foreign key(grade_id) references class_grade(gid) on delete cascade on update cascade ); insert into class(caption, grade_id) values ('一年一班',1), ('一年二班',1), ('二年一班',2), ('二年二班',2), ('三年一班',3), ('四年一班',4), ('五年一班',5); create table student ( sid int primary key auto_increment, sname char(20), gender enum('男', '女') not null, class_id int, foreign key(class_id) references class(cid) on delete cascade on update cascade ); insert into student(sname,gender,class_id) values ('乔丹','女',1), ('艾弗森','女',1), ('科比','男',2), ('curry','男',2), ('james','男',3), ('李瑞','女',4), ('白雪','女',5), ('无敌','男',5), ('天剑','男',6), ('egon','女',7), ('alex','男',7); create table score ( sid int primary key auto_increment, student_id int, course_id int, score int, foreign key(student_id) references student(sid) on delete cascade on update cascade, foreign key(course_id) references course(cid) on delete cascade on update cascade ); insert into score(student_id, course_id, score) values (1,1,60), (1,2,59), (1,3,58), (1,4,71), (1,5,68), (1,6,100), (2,1,90), (2,2,99), (2,3,71), (2,4,68), (2,5,92), (2,6,88), (3,1,23), (3,2,55), (3,3,72), (3,4,88), (3,5,92), (3,6,12), (4,2,65), (4,4,78), (4,5,34), (5,2,75), (5,4,38), (5,5,44), (6,2,23), (6,4,32), (6,5,0), (7,1,78), (7,3,60), (7,6,45), (8,1,43), (8,3,65), (8,6,99), (9,2,56), (9,3,69), (9,5,78), (10,2,43), (10,3,69), (10,5,90), (11,2,90), (11,3,89), (11,5,100); create table teach2cls ( tcid int primary key auto_increment, tid int, cid int, foreign key(tid) references teacher(tid) on delete cascade on update cascade, foreign key(cid) references class(cid) on delete cascade on update cascade ); insert into teach2cls(tid, cid) values # 五个老师、七个班级 (1,1), (1,2), (1,5), (1,7), (2,2), (2,3), (2,4), (2,6), (3,1), (3,2), (3,4), (3,5), (3,6), (4,2), (4,4), (4,7), (5,5), (5,6), (5,7); -- 2、查询学生总人数； select count(sid) as total_num from student; +-----------+ | total_num | +-----------+ | 11 | +-----------+ -- 3、查询“生物”课程和“物理”课程成绩都及格的学生id和姓名； select sid, sname from student where sid in ( select score.student_id # 先找到学习了这两们课且都及格学生的id from score inner join course on score.course_id=course.cid where course.cname in ( '生物', '物理' ) and score.score >=60 group by score.student_id having count(course_id) =2 ); +-----+-----------+ | sid | sname | +-----+-----------+ | 2 | 艾弗森 | | 7 | 白雪 | +-----+-----------+ -- 4、查询每个年级的班级数，取出班级数最多的前三个年级； select gname,count(class.cid) from class_grade inner join class on class.grade_id=class_grade.gid group by gid order by count(cid) DESC limit 3; +-----------+------------------+ | gname | count(class.cid) | +-----------+------------------+ | 一年级 | 2 | | 二年级 | 2 | | 四年级 | 1 | +-----------+------------------+ -- 5、查询平均成绩最高和最低的学生的id和姓名以及平均成绩； select * from ( select avg(score) as avg_score from score group by student_id order by avg_score ASC limit 1 ) t1 union select * from (select avg(score) as avg_score from score group by student_id order by avg_score DESC limit 1) t2; +-----------+ | avg_score | +-----------+ | 18.3333 | | 93.0000 | +-----------+ select student_id, concat(student.sname) as student_name, avg(score) from student inner join score on score.student_id=student.sid group by student_id having avg(score) in ( select * from ( select avg(score) as avg_score from score group by student_id order by avg_score ASC limit 1 ) t1 union select * from( select avg(score) as avg_score from score group by student_id order by avg_score DESC limit 1) t2 ); # 由于最小成绩是无限小数，无法显示 +------------+--------------+------------+ | student_id | student_name | avg(score) | +------------+--------------+------------+ | 11 | alex | 93.0000 | +------------+--------------+------------+ -- 6、查询每个年级的学生人数； select grade_id, count(sid) from student left join class on student.class_id=class.cid group by grade_id; +----------+------------+ | grade_id | count(sid) | +----------+------------+ | 1 | 4 | | 2 | 2 | | 3 | 2 | | 4 | 1 | | 5 | 2 | +----------+------------+ select gname, t1.stu_num as stu_num from class_grade inner join (select grade_id, count(sid) as stu_num from student left join class on student.class_id=class.cid group by grade_id) as t1 on class_grade.gid=t1.grade_id; +-----------+---------+ | gname | stu_num | +-----------+---------+ | 一年级 | 4 | | 二年级 | 2 | | 三年级 | 2 | | 四年级 | 1 | | 五年级 | 2 | +-----------+---------+ -- 7、查询每位学生的学号，姓名，选课数，平均成绩； select student.sid, concat(student.sname), count(course_id) as course_num, avg(score) as avg_score from student inner join score on student.sid=score.student_id group by student.sid; +-----+-----------------------+------------+-----------+ | sid | concat(student.sname) | course_num | avg_score | +-----+-----------------------+------------+-----------+ | 1 | 乔丹 | 6 | 69.3333 | | 2 | 艾弗森 | 6 | 84.6667 | | 3 | 科比 | 6 | 57.0000 | | 4 | curry | 3 | 59.0000 | | 5 | james | 3 | 52.3333 | | 6 | 李瑞 | 3 | 18.3333 | | 7 | 白雪 | 3 | 61.0000 | | 8 | 无敌 | 3 | 69.0000 | | 9 | 天剑 | 3 | 67.6667 | | 10 | egon | 3 | 67.3333 | | 11 | alex | 3 | 93.0000 | +-----+-----------------------+------------+-----------+ -- 8、查询学生编号为“2”的学生的姓名、该学生成绩最高的课程名、成绩最低的课程名及分数； # score——》student——》course select student.sname, course.cname, score.score from score left join student on score.student_id=student.sid left join course on score.course_id=course.cid where student.sid=2 and score in ( select * from ( select max(score) from score where student_id=2) t1 union select * from ( select min(score) from score where student_id=2) t2 ); +-----------+--------+-------+ | sname | cname | score | +-----------+--------+-------+ | 艾弗森 | 体育 | 99 | | 艾弗森 | 语文 | 68 | +-----------+--------+-------+ -- 9、查询姓“李”的老师的个数和所带班级数； select concat(teacher.tname), count(distinct teacher.tid) as teacher_num, count(teach2cls.cid) as class_num from teacher inner join teach2cls on teacher.tid=teach2cls.tid where tname like '李%' group by teacher.tid; +-----------------------+-------------+-----------+ | concat(teacher.tname) | teacher_num | class_num | +-----------------------+-------------+-----------+ | 李四 | 1 | 4 | +-----------------------+-------------+-----------+ -- 10、查询班级数小于5的年级id和年级名； select gid, gname from class_grade where gid in ( select grade_id from class group by grade_id having count(cid) < 5 ) ; +-----+-----------+ | gid | gname | +-----+-----------+ | 1 | 一年级 | | 2 | 二年级 | | 3 | 三年级 | | 4 | 四年级 | | 5 | 五年级 | +-----+-----------+ -- 11、查询班级信息，包括班级id、班级名称、年级、年级级别(12为低年级，34为中年级，56为高年级)，示例结果如下； # mysql中case when then else end的用法 select class.cid, class.caption, class_grade.gname, case # 如果 when class_grade.gid between 1 and 2 then '低年级' # when后接条件，then后接返回值 when class_grade.gid between 3 and 4 then '中年级' when class_grade.gid between 5 and 6 then '高年级' else 0 # 其他的返回值 end as '年级级别' # end代表结束，自定义为'年级级别' from class inner join class_grade on class.grade_id=class_grade.gid; +-----+--------------+-----------+--------------+ | cid | caption | gname | 年级级别 | +-----+--------------+-----------+--------------+ | 1 | 一年一班 | 一年级 | 低年级 | | 2 | 一年二班 | 一年级 | 低年级 | | 3 | 二年一班 | 二年级 | 低年级 | | 4 | 二年二班 | 二年级 | 低年级 | | 5 | 三年一班 | 三年级 | 中年级 | | 6 | 四年一班 | 四年级 | 中年级 | | 7 | 五年一班 | 五年级 | 高年级 | +-----+--------------+-----------+--------------+ -- 12、查询学过“张三”老师2门课以上的同学的学号、姓名； select sid, sname from student where sid in ( select student_id from score where course_id in ( select cid from course where teacher_id=( select tid from teacher where tname='张三' ) ) group by student_id having count(course_id)>=2 ); +-----+-----------+ | sid | sname | +-----+-----------+ | 1 | 乔丹 | | 2 | 艾弗森 | | 3 | 科比 | +-----+-----------+ -- 13、查询教授课程超过2门的老师的id和姓名； select tid, tname from teacher where tid in ( select teacher_id from course group by teacher_id having count(cid) >= 2 ); +-----+--------+ | tid | tname | +-----+--------+ | 1 | 张三 | +-----+--------+ -- 14、查询学过编号“1”课程和编号“2”课程的同学的学号、姓名； select sid, sname from student where sid in ( select student_id from score where course_id in (1,2) group by student_id ); +-----+-----------+ | sid | sname | +-----+-----------+ | 1 | 乔丹 | | 2 | 艾弗森 | | 3 | 科比 | | 4 | curry | | 5 | james | | 6 | 李瑞 | | 7 | 白雪 | | 8 | 无敌 | | 9 | 天剑 | | 10 | egon | | 11 | alex | +-----+-----------+ -- 15、查询没有带过高年级的老师id和姓名； select * from teacher where tid not in ( select tid from teach2cls inner join class on teach2cls.cid=class.cid where class.grade_id in (5,6) ); +-----+--------+ | tid | tname | +-----+--------+ | 2 | 李四 | | 3 | 王五 | +-----+--------+ -- 16、查询学过“张三”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 cid # 张三教过的班级id from teach2cls inner join teacher on teach2cls.tid=teacher.tid where teacher.tname='张三' ); +-----+-----------+ | sid | sname | +-----+-----------+ | 1 | 乔丹 | | 2 | 艾弗森 | | 3 | 科比 | | 4 | curry | | 7 | 白雪 | | 8 | 无敌 | | 10 | egon | | 11 | alex | +-----+-----------+ -- 17、查询带过超过2个班级的老师的id和姓名； select * from teacher where tid in ( select tid from teach2cls group by tid having count(cid) >= 2 ); +-----+--------+ | tid | tname | +-----+--------+ | 1 | 张三 | | 2 | 李四 | | 3 | 王五 | | 4 | 赵六 | | 5 | 马七 | +-----+--------+ -- 18、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 sid, sname from student where sid in( select t1.student_id from (select student_id, score as score_1 from score where course_id=1) as t1 inner join (select student_id, score as score_2 from score where course_id=2) as t2 on t1.student_id=t2.student_id where t2.score_2 > t1.score_1 ); +-----+-----------+ | sid | sname | +-----+-----------+ | 2 | 艾弗森 | | 3 | 科比 | +-----+-----------+ -- 19、查询所带班级数最多的老师id和姓名； select * from teacher where tid in ( select tid # 考虑带最多班级的是多个老师，老师的tid from teach2cls group by tid having count(cid)=( select # 得到最多班级数量 count(cid) from teach2cls group by tid order by count(cid) desc limit 1 ) ); +-----+--------+ | tid | tname | +-----+--------+ | 3 | 王五 | +-----+--------+ -- 20、查询有课程成绩小于60分的同学的学号、姓名； select sid, sname from student where sid in ( select distinct student_id from score where score.score < 60 ); +-----+--------+ | sid | sname | +-----+--------+ | 1 | 乔丹 | | 3 | 科比 | | 4 | curry | | 5 | james | | 6 | 李瑞 | | 7 | 白雪 | | 8 | 无敌 | | 9 | 天剑 | | 10 | egon | +-----+--------+ -- 21、查询没有学全所有课的同学的学号、姓名； select sid, sname from student where sid in ( select student_id from score group by student_id having count(course_id) < ( select count(cid) from course ) ); +-----+--------+ | sid | sname | +-----+--------+ | 4 | curry | | 5 | james | | 6 | 李瑞 | | 7 | 白雪 | | 8 | 无敌 | | 9 | 天剑 | | 10 | egon | | 11 | alex | +-----+--------+ -- 22、查询至少有一门课与学号为“1”的同学所学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 # 找出学号1锁学得所有课程 from score where student_id=1 ) and student_id!=1 # 排除掉学号为1的学生 ); +-----+-----------+ | sid | sname | +-----+-----------+ | 2 | 艾弗森 | | 3 | 科比 | | 4 | curry | | 5 | james | | 6 | 李瑞 | | 7 | 白雪 | | 8 | 无敌 | | 9 | 天剑 | | 10 | egon | | 11 | alex | +-----+-----------+ -- 23、查询至少学过学号为“1”同学所选课程中任意一门课的其他同学学号和姓名； select sid, sname from student where sid in ( select distinct student_id from score where course_id in ( select course_id # 找出学号1锁学得所有课程 from score where student_id=1 ) and student_id!=1 # 排除掉学号为1的学生 ); +-----+-----------+ | sid | sname | +-----+-----------+ | 2 | 艾弗森 | | 3 | 科比 | | 4 | curry | | 5 | james | | 6 | 李瑞 | | 7 | 白雪 | | 8 | 无敌 | | 9 | 天剑 | | 10 | egon | | 11 | alex | +-----+-----------+ -- 24、查询和“2”号同学学习的课程完全相同的其他同学的学号和姓名； select sid, sname from student where sid in ( select score.student_id from score inner join (select course_id # 课程id from score where student_id = 2) as t1 where score.course_id = t1.course_id and score.student_id != 2 group by score.student_id having count(score.course_id) = ( select # 学号2所学课程总数 count(course_id) from score where student_id =2 ) ); +-----+--------+ | sid | sname | +-----+--------+ | 1 | 乔丹 | | 3 | 科比 | +-----+--------+ -- 25、删除学习“张三”老师课的score表记录； select course.cid from course left join teacher on course.teacher_id=teacher.tid where teacher.tname='张三'; +-----+ | cid | +-----+ | 1 | | 2 | +-----+ # 删除course_id为1，2的记录 delete from score where course_id in ( select course.cid from course left join teacher on course.teacher_id=teacher.tid where teacher.tname='张三' ); +-----+------------+-----------+-------+ | sid | student_id | course_id | score | +-----+------------+-----------+-------+ | 3 | 1 | 3 | 58 | | 4 | 1 | 4 | 71 | | 5 | 1 | 5 | 68 | | 6 | 1 | 6 | 100 | | 9 | 2 | 3 | 71 | | 10 | 2 | 4 | 68 | | 11 | 2 | 5 | 92 | | 12 | 2 | 6 | 88 | | 15 | 3 | 3 | 72 | | 16 | 3 | 4 | 88 | | 17 | 3 | 5 | 92 | | 18 | 3 | 6 | 12 | | 20 | 4 | 4 | 78 | | 21 | 4 | 5 | 34 | | 23 | 5 | 4 | 38 | | 24 | 5 | 5 | 44 | | 26 | 6 | 4 | 32 | | 27 | 6 | 5 | 0 | | 29 | 7 | 3 | 60 | | 30 | 7 | 6 | 45 | | 32 | 8 | 3 | 65 | | 33 | 8 | 6 | 99 | | 35 | 9 | 3 | 69 | | 36 | 9 | 5 | 78 | | 38 | 10 | 3 | 69 | | 39 | 10 | 5 | 90 | | 41 | 11 | 3 | 89 | | 42 | 11 | 5 | 100 | +-----+------------+-----------+-------+ -- 26、向score表中插入一些记录，这些记录要求符合以下条件：①没有上过编号“2”课程的同学学号；②插入“2”号课程的平均成绩； select sid from student where sid not in ( select student_id from score where course_id =2 ); +-----+ | sid | +-----+ | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | | 7 | | 8 | | 9 | | 10 | | 11 | +-----+ select avg(score) as avg_score from score where course_id = 2; +-----------+ | avg_score | +-----------+ | NULL | +-----------+ insert into score(student_id, course_id, score) select t1.sid, 2, t2.avg_score from (select sid from student where sid not in ( select student_id from score where course_id =2 ) ) as t1, (select avg(score) as avg_score from score where course_id = 2 ) as t2; # 增加以下记录 +-----+------------+-----------+-------+ | sid | student_id | course_id | score | +-----+------------+-----------+-------+ | 3 | 1 | 3 | 58 | ....... | | 42 | 11 | 5 | 100 | | 43 | 1 | 2 | NULL | | 44 | 2 | 2 | NULL | | 45 | 3 | 2 | NULL | | 46 | 4 | 2 | NULL | | 47 | 5 | 2 | NULL | | 48 | 6 | 2 | NULL | | 49 | 7 | 2 | NULL | | 50 | 8 | 2 | NULL | | 51 | 9 | 2 | NULL | | 52 | 10 | 2 | NULL | | 53 | 11 | 2 | NULL | +-----+------------+-----------+-------+ # 将这些空值都修改为73 -- 27、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； # 这个题难度很大 select main_score.student_id, (select score.score from score left join course on score.course_id=course.cid where course.cname='语文' and score.student_id=main_score.student_id) as chinese, (select score.score from score left join course on score.course_id=course.cid where course.cname='数学' and score.student_id=main_score.student_id) as math, (select score.score from score left join course on score.course_id=course.cid where course.cname='英语' and score.student_id=main_score.student_id) as english, count(main_score.course_id), avg(main_score.score) from score as main_score group by main_score.student_id order by # 注意order的拼写 avg(main_score.score) ASC; +------------+---------+------+---------+-----------------------------+-----------------------+ | student_id | chinese | math | english | count(main_score.course_id) | avg(main_score.score) | +------------+---------+------+---------+-----------------------------+-----------------------+ | 6 | 32 | 0 | NULL | 3 | 35.0000 | | 5 | 38 | 44 | NULL | 3 | 51.6667 | | 7 | NULL | NULL | NULL | 3 | 59.3333 | | 4 | 78 | 34 | NULL | 3 | 61.6667 | | 3 | 88 | 92 | NULL | 5 | 67.4000 | | 9 | NULL | 78 | NULL | 3 | 73.3333 | | 1 | 71 | 68 | NULL | 5 | 74.0000 | | 10 | NULL | 90 | NULL | 3 | 77.3333 | | 2 | 68 | 92 | NULL | 5 | 78.4000 | | 8 | NULL | NULL | NULL | 3 | 79.0000 | | 11 | NULL | 100 | NULL | 3 | 87.3333 | +------------+---------+------+---------+-----------------------------+-----------------------+ -- 28、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(score.score) as max_score, min(score.score) as min_score from course left join score on course.cid=score.course_id group by score.course_id; +-----------+-----------+-----------+ | course_id | max_score | min_score | +-----------+-----------+-----------+ | NULL | NULL | NULL | | 2 | 73 | 73 | | 3 | 89 | 58 | | 4 | 88 | 32 | | 5 | 100 | 0 | | 6 | 100 | 12 | +-----------+-----------+-----------+ -- 29、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； select course_id, avg(score) as avg_score from score group by course_id order by avg(score) desc; +-----------+-----------+ | course_id | avg_score | +-----------+-----------+ | 2 | 73.0000 | | 3 | 69.1250 | | 6 | 68.8000 | | 5 | 66.4444 | | 4 | 62.5000 | +-----------+-----------+ -- 30、课程平均分从高到低显示（显示任课老师); select t2.cid, t2.cname, t2.avg_score, teacher.tname from teacher right join ( select course.cid, course.cname, t1.avg_score, course.teacher_id from course inner join ( select course_id, avg(score) avg_score from score group by course_id ) as t1 on course.cid=t1.course_id ) as t2 on teacher.tid=t2.teacher_id order by t2.avg_score desc; +-----+--------+-----------+--------+ | cid | cname | avg_score | tname | +-----+--------+-----------+--------+ | 2 | 体育 | 73.0000 | 张三 | | 3 | 物理 | 69.1250 | 李四 | | 6 | 外语 | 68.8000 | 马七 | | 5 | 数学 | 66.4444 | 赵六 | | 4 | 语文 | 62.5000 | 王五 | +-----+--------+-----------+--------+ -- 31、查询各科成绩前三名的记录(不考虑成绩并列情况) select score.sid,score.course_id,score.score,T.first_num,T.second_num from score left join ( select sid, (select score from score as s2 where s2.course_id = s1.course_id order by score desc limit 0,1) as first_num, (select score from score as s2 where s2.course_id = s1.course_id order by score desc limit 3,1) as second_num from score as s1 ) as T on score.sid =T.sid where score.score <= T.first_num and score.score >= T.second_num; +-----+-----------+-------+-----------+------------+ | sid | course_id | score | first_num | second_num | +-----+-----------+-------+-----------+------------+ | 43 | 2 | 73 | 73 | 73 | | 44 | 2 | 73 | 73 | 73 | | 45 | 2 | 73 | 73 | 73 | | 46 | 2 | 73 | 73 | 73 | | 47 | 2 | 73 | 73 | 73 | | 48 | 2 | 73 | 73 | 73 | | 49 | 2 | 73 | 73 | 73 | | 50 | 2 | 73 | 73 | 73 | | 51 | 2 | 73 | 73 | 73 | | 52 | 2 | 73 | 73 | 73 | | 53 | 2 | 73 | 73 | 73 | | 9 | 3 | 71 | 89 | 69 | | 15 | 3 | 72 | 89 | 69 | | 35 | 3 | 69 | 89 | 69 | | 38 | 3 | 69 | 89 | 69 | | 41 | 3 | 89 | 89 | 69 | | 4 | 4 | 71 | 88 | 68 | | 10 | 4 | 68 | 88 | 68 | | 16 | 4 | 88 | 88 | 68 | | 20 | 4 | 78 | 88 | 68 | | 11 | 5 | 92 | 100 | 90 | | 17 | 5 | 92 | 100 | 90 | | 39 | 5 | 90 | 100 | 90 | | 42 | 5 | 100 | 100 | 90 | | 6 | 6 | 100 | 100 | 45 | | 12 | 6 | 88 | 100 | 45 | | 30 | 6 | 45 | 100 | 45 | | 33 | 6 | 99 | 100 | 45 | +-----+-----------+-------+-----------+------------+ # 需要进一步改进 select course_id, (select score from score as s2 where s2.course_id = s1.course_id order by score desc limit 1) as first_num, (select score from score as s2 where s2.course_id = s1.course_id order by score desc limit 1,1) as secend_num, (select score from score as s2 where s2.course_id = s1.course_id order by score desc limit 2,1) as third_num from score as s1; +-----------+-----------+------------+-----------+ | course_id | first_num | secend_num | third_num | +-----------+-----------+------------+-----------+ | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 2 | 73 | 73 | 73 | | 3 | 89 | 72 | 71 | | 3 | 89 | 72 | 71 | | 3 | 89 | 72 | 71 | | 3 | 89 | 72 | 71 | | 3 | 89 | 72 | 71 | | 3 | 89 | 72 | 71 | | 3 | 89 | 72 | 71 | | 3 | 89 | 72 | 71 | | 4 | 88 | 78 | 71 | | 4 | 88 | 78 | 71 | | 4 | 88 | 78 | 71 | | 4 | 88 | 78 | 71 | | 4 | 88 | 78 | 71 | | 4 | 88 | 78 | 71 | | 5 | 100 | 92 | 92 | | 5 | 100 | 92 | 92 | | 5 | 100 | 92 | 92 | | 5 | 100 | 92 | 92 | | 5 | 100 | 92 | 92 | | 5 | 100 | 92 | 92 | | 5 | 100 | 92 | 92 | | 5 | 100 | 92 | 92 | | 5 | 100 | 92 | 92 | | 6 | 100 | 99 | 88 | | 6 | 100 | 99 | 88 | | 6 | 100 | 99 | 88 | | 6 | 100 | 99 | 88 | | 6 | 100 | 99 | 88 | +-----------+-----------+------------+-----------+ select course_id from (select course_id, (select score from score as s2 where s2.course_id = s1.course_id order by score desc limit 1) as first_num, (select score from score as s2 where s2.course_id = s1.course_id order by score desc limit 1,1) as secend_num, (select score from score as s2 where s2.course_id = s1.course_id order by score desc limit 2,1) as third_num from score as s1 ) as T group by course_id; -- 32、查询每门课程被选修的学生数； select course_id, count(student_id) from score group by course_id; +-----------+-------------------+ | course_id | count(student_id) | +-----------+-------------------+ | 2 | 11 | | 3 | 8 | | 4 | 6 | | 5 | 9 | | 6 | 5 | +-----------+-------------------+ -- 33、查询选修了2门以上课程的全部学生的学号和姓名； select sid, sname from student where sid in ( select student_id from score group by student_id having count(course_id) > 2 ); +-----+-----------+ | sid | sname | +-----+-----------+ | 1 | 乔丹 | | 2 | 艾弗森 | | 3 | 科比 | | 4 | curry | | 5 | james | | 6 | 李瑞 | | 7 | 白雪 | | 8 | 无敌 | | 9 | 天剑 | | 10 | egon | | 11 | alex | +-----+-----------+ -- 34、查询男生、女生的人数，按倒序排列； select gender, count(sid) from student group by gender order by count(sid) desc; +--------+------------+ | gender | count(sid) | +--------+------------+ | 男 | 6 | | 女 | 5 | +--------+------------+ -- 35、查询姓“张”的学生名单； select * from student where sname='张%'; Empty set (0.00 sec) -- 36、查询同名同姓学生名单，并统计同名人数； select sname, count(sid) from student group by sname having count(sid) > 1; Empty set (0.00 sec) -- 37、查询每门课程的平均成绩，结果按平均成绩升序排列，平均成绩相同时，按课程号降序排列； select course_id, avg(score) from score group by course_id order by avg(score), # 两种排序规则需要用逗号分隔 course_id DESC; +-----------+------------+ | course_id | avg(score) | +-----------+------------+ | 4 | 62.5000 | | 5 | 66.4444 | | 6 | 68.8000 | | 3 | 69.1250 | | 2 | 73.0000 | +-----------+------------+ -- 38、查询课程名称为“数学”，且分数低于60的学生姓名和分数； select student.sname, score.score from score inner join student on score.student_id=student.sid where score.course_id in ( select cid from course where cname='数学' ); +-----------+-------+ | sname | score | +-----------+-------+ | 乔丹 | 68 | | 艾弗森 | 92 | | 科比 | 92 | | curry | 34 | | james | 44 | | 李瑞 | 0 | | 天剑 | 78 | | egon | 90 | | alex | 100 | +-----------+-------+ -- 39、查询课程编号为“3”且课程成绩在80分以上的学生的学号和姓名； select sid, sname from student where sid in ( select student_id from score where course_id=3 and score>=80 ); +-----+-------+ | sid | sname | +-----+-------+ | 11 | alex | +-----+-------+ -- 40、求选修了课程的学生人数 select course_id, count(student_id) from score group by course_id; +-----------+-------------------+ | course_id | count(student_id) | +-----------+-------------------+ | 2 | 11 | | 3 | 8 | | 4 | 6 | | 5 | 9 | | 6 | 5 | +-----------+-------------------+ -- 41、查询选修“王五”老师所授课程的学生中，成绩最高和最低的学生姓名及其成绩； select * from (select * from student inner join (select student_id, score from score where course_id in ( select cid from teacher inner join course on teacher.tid=course.teacher_id where tname='王五' ) ) as t1 on student.sid=t1.student_id order by score limit 1 ) as t2 union select * from (select * from student inner join (select student_id, score from score where course_id in ( select cid from teacher inner join course on teacher.tid=course.teacher_id where tname='王五' ) ) as t1 on student.sid=t1.student_id order by score DESC limit 1 ) as t3; +-----+--------+--------+----------+------------+-------+ | sid | sname | gender | class_id | student_id | score | +-----+--------+--------+----------+------------+-------+ | 6 | 李瑞 | 女 | 4 | 6 | 32 | | 3 | 科比 | 男 | 2 | 3 | 88 | +-----+--------+--------+----------+------------+-------+ -- 42、查询各个课程及相应的选修人数； select cid, cname, t1.stu_num from course right join (select course_id, count(student_id) as stu_num from score group by course_id) as t1 on course.cid=t1.course_id; +------+--------+---------+ | cid | cname | stu_num | +------+--------+---------+ | 2 | 体育 | 11 | | 3 | 物理 | 8 | | 4 | 语文 | 6 | | 5 | 数学 | 9 | | 6 | 外语 | 5 | +------+--------+---------+ -- 43、查询不同课程但成绩相同的学生的学号、课程号、学生成绩； select * from score where score in ( select score # 找到不同课程但是有相同分数的成绩数值 from score group by score having count(course_id)>1 ) order by score; +-----+------------+-----------+-------+ | sid | student_id | course_id | score | +-----+------------+-----------+-------+ | 5 | 1 | 5 | 68 | | 10 | 2 | 4 | 68 | | 35 | 9 | 3 | 69 | | 38 | 10 | 3 | 69 | | 4 | 1 | 4 | 71 | | 9 | 2 | 3 | 71 | | 43 | 1 | 2 | 73 | | 44 | 2 | 2 | 73 | | 45 | 3 | 2 | 73 | | 46 | 4 | 2 | 73 | | 47 | 5 | 2 | 73 | | 48 | 6 | 2 | 73 | | 49 | 7 | 2 | 73 | | 50 | 8 | 2 | 73 | | 51 | 9 | 2 | 73 | | 52 | 10 | 2 | 73 | | 53 | 11 | 2 | 73 | | 20 | 4 | 4 | 78 | | 36 | 9 | 5 | 78 | | 12 | 2 | 6 | 88 | | 16 | 3 | 4 | 88 | | 11 | 2 | 5 | 92 | | 17 | 3 | 5 | 92 | | 6 | 1 | 6 | 100 | | 42 | 11 | 5 | 100 | +-----+------------+-----------+-------+ -- 44、查询每门课程成绩最好的前两名学生id和姓名； select student.sid, student.sname, t2.course_id, t2.score, t2.first_score, t2.second_score from student inner join ( # 这里会出现成绩相同的情况，录入了超过了两名的学生！！ select score.student_id, score.course_id, score.score, t1.first_score, t1.second_score from score inner join ( select s1.sid, (select s2.score from score as s2 where s1.course_id = s2.course_id order by s2.score desc limit 0,1) as first_score, (select s3.score from score as s3 where s1.course_id = s3.course_id order by s3.score desc limit 1,1) as second_score from score as s1 ) as t1 on score.sid = t1.sid where score.score in ( # ？？在这，会超过两个！！ t1.first_score, t1.second_score ) ) as t2 on student.sid = t2.student_id; +-----+-----------+-----------+-------+-------------+--------------+ | sid | sname | course_id | score | first_score | second_score | +-----+-----------+-----------+-------+-------------+--------------+ | 1 | 乔丹 | 2 | 73 | 73 | 73 | | 2 | 艾弗森 | 2 | 73 | 73 | 73 | | 3 | 科比 | 2 | 73 | 73 | 73 | | 4 | curry | 2 | 73 | 73 | 73 | | 5 | james | 2 | 73 | 73 | 73 | | 6 | 李瑞 | 2 | 73 | 73 | 73 | | 7 | 白雪 | 2 | 73 | 73 | 73 | | 8 | 无敌 | 2 | 73 | 73 | 73 | | 9 | 天剑 | 2 | 73 | 73 | 73 | | 10 | egon | 2 | 73 | 73 | 73 | | 11 | alex | 2 | 73 | 73 | 73 | | 3 | 科比 | 3 | 72 | 89 | 72 | | 11 | alex | 3 | 89 | 89 | 72 | | 3 | 科比 | 4 | 88 | 88 | 78 | | 4 | curry | 4 | 78 | 88 | 78 | | 2 | 艾弗森 | 5 | 92 | 100 | 92 | | 3 | 科比 | 5 | 92 | 100 | 92 | | 11 | alex | 5 | 100 | 100 | 92 | | 1 | 乔丹 | 6 | 100 | 100 | 99 | | 8 | 无敌 | 6 | 99 | 100 | 99 | +-----+-----------+-----------+-------+-------------+--------------+ -- 45、检索至少选修两门课程的学生学号； select student_id from score group by student_id having count(course_id)>=2; +------------+ | student_id | +------------+ | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | | 7 | | 8 | | 9 | | 10 | | 11 | +------------+ -- 46、查询没有学生选修的课程的课程号和课程名； select cid, cname from course where cid not in ( select course_id from score group by course_id ); +-----+--------+ | cid | cname | +-----+--------+ | 1 | 生物 | +-----+--------+ -- 47、查询没带过任何班级的老师id和姓名； select tid, tname from teacher where tid not in( select tid from teach2cls group by tid ); Empty set (0.00 sec) -- 48、查询有两门以上课程超过80分的学生id及其平均成绩； select student_id, avg(score) as avg_score from score where score.student_id in (select student_id # 找到有两门课大于80的学号 from (select * from score where score>80) as t1 group by student_id having count(course_id) >= 2 ) group by student_id; +------------+-----------+ | student_id | avg_score | +------------+-----------+ | 2 | 78.4000 | | 3 | 67.4000 | | 11 | 87.3333 | +------------+-----------+ -- 49、检索“3”课程分数小于60，按分数降序排列的同学学号； select student_id from score where course_id=3 and score<60 order by score DESC; +------------+ | student_id | +------------+ | 1 | +------------+ -- 50、删除编号为“2”的同学的“1”课程的成绩； select sid from score where student_id=2 and course_id=1; delete from score where sid in ( select sid from score where student_id=2 and course_id=1 ); ERROR 1093 (HY000): You can't specify target table 'score' for update in FROM clause' delete from score where sid in ( select t1.sid from ( select sid from score where student_id=2 and course_id=1 ) as t1 ); Query OK, 0 rows affected (0.00 sec) -- 51、查询同时选修了物理课和生物课的学生id和姓名； select cid from course where cname='物理' or cname='生物'; +-----+--------+------------+ | cid | cname | teacher_id | +-----+--------+------------+ | 1 | 生物 | 1 | | 3 | 物理 | 2 | +-----+--------+------------+ select sid, sname from student where sid in ( select student_id FROM score where course_id in ( select cid from course where cname='物理' or cname='生物' ) group by student_id having count(course_id)=2 ); Empty set (0.00 sec)