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查询所有大于60分的学生的姓名和学号 (DISTINCT: 去重)
select student.sname,score.sid from score left join student on student_id = student.sid where number >60; mysql> select student.sname,score.sid from score left join student on student_id = student.sid where number >60; +-------+-----+ | sname | sid | +-------+-----+ | 铁锤 | 3 | +-------+-----+
-- 2.查询每个老师教授的课程数量 和 老师信息
select teacher.tid,teacher.tname,count(course.teacher_id) from teacher left join course on teacher.tid=teacher_id group by course.teacher_id;
mysql> select teacher.tid,teacher.tname,count(course.teacher_id) from teacher left join course on teacher.tid=teacher_id group by course.teacher_id;
+-----+--------+--------------------------+
| tid | tname | count(course.teacher_id) |
+-----+--------+--------------------------+
| 1 | 波多 | 2 |
| 2 | 苍空 | 1 |
| 3 | 饭岛 | 1 |
| 4 | 张磊 | 2 |
| 5 | 李平 | 1 |
| 6 | 刘海燕 | 1 |
| 7 | 朱云海 | 1 |
| 8 | 李杰 | 1 |
+-----+--------+--------------------------+
-- 3. 查询学 生的信息以及学生所在的班级信息
select sid,sname,gender,class.caption from student left join class on class_id =class.cid;
mysql> select student.sid,student.sname,student.gender,class.caption from student left join class on class_id =class.cid;
+-----+-------+--------+----------+
| sid | sname | gender | caption |
+-----+-------+--------+----------+
| 1 | 钢蛋 | 女 | 三年二班 |
| 2 | 铁锤 | 女 | 三年二班 |
| 3 | 山炮 | 男 | 一年三班 |
+-----+-------+--------+----------+
-- 4、学生中男生的个数和女生的个数
select gender,count(gender) from student group by gender;
mysql> select student.sid,student.sname,student.gender,class.caption from student left join class on class_id =class.cid;
+-----+-------+--------+----------+
| sid | sname | gender | caption |
+-----+-------+--------+----------+
| 1 | 钢蛋 | 女 | 三年二班 |
| 2 | 铁锤 | 女 | 三年二班 |
| 3 | 山炮 | 男 | 一年三班 |
+-----+-------+--------+----------+
-- 5、获取所有学习'生物'的学生的学号和成绩；姓名
select student.sid,student.sname,number from student left join score on student.sid = student_id left join course on course.cid=corse_id where course.cid =1;
mysql> select student.sid,student.sname,number from student left join score on student.sid = student_id left join course on course.cid=corse_id where course.cid =1;
+-----+-------+--------+
| sid | sname | number |
+-----+-------+--------+
| 1 | 钢蛋 | 60 |
+-----+-------+--------+
-- 6、查询平均成绩大于60分的同学的学号和平均成绩；
select student.sid,avg(number) from score left join student on student_id=student.sid group by student.sid having avg(number)>60;
mysql> select student.sid,avg(number) from score left join student on student_id=student.sid group by student.sid having avg(number)>60;
+------+-------------+
| sid | avg(number) |
+------+-------------+
| 1 | 72.2500 |
| 2 | 67.5000 |
| 3 | 93.3333 |
+------+-------------+
-- 7、查询姓“李”的老师的个数；
select count(tname) as '李姓老师的个数' from teacher where tname like '李%';
mysql> select count(tname) as '李姓老师的个数' from teacher where tname like '李%';
+----------------+
| 李姓老师的个数 |
+----------------+
| 2 |
+----------------+
-- 8、查询课程成绩小于60分的同学的学号、姓名；
select student.sid,student.sname from student left join score on student.sid=student_id where number<60;
mysql> select student.sid,student.sname from student left join score on student.sid=student_id where number<60;
+-----+-------+
| sid | sname |
+-----+-------+
| 1 | 钢蛋 |
| 2 | 铁锤 |
+-----+-------+
-- 9. 删除学习“叶平”老师课的SC表记录
delete from teacher where tname ='叶平';
mysql> select * from teacher;
+-----+--------+
| tid | tname |
+-----+--------+
| 1 | 波多 |
| 2 | 苍空 |
| 3 | 饭岛 |
| 4 | 张磊 |
| 5 | 李平 |
| 6 | 刘海燕 |
| 7 | 朱云海 |
| 8 | 李杰 |
| 9 | 叶平 |
+-----+--------+
mysql> delete from teacher where tname ='叶平';
Query OK, 1 row affected (0.10 sec)
mysql> select * from teacher;
+-----+--------+
| tid | tname |
+-----+--------+
| 1 | 波多 |
| 2 | 苍空 |
| 3 | 饭岛 |
| 4 | 张磊 |
| 5 | 李平 |
| 6 | 刘海燕 |
| 7 | 朱云海 |
| 8 | 李杰 |
+-----+--------+
-- 10.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 corse_id,max(number),min(number) from score left join course on course.cid=corse_id group by corse_id;
mysql> select corse_id,max(number),min(number) from score left join course on course.cid=corse_id group by corse_id;
+----------+-------------+-------------+
| corse_id | max(number) | min(number) |
+----------+-------------+-------------+
| 1 | 60 | 60 |
| 2 | 100 | 59 |
| 3 | 80 | 80 |
| 4 | 90 | 90 |
| 5 | 70 | 70 |
| 6 | 80 | 80 |
| 7 | 80 | 80 |
| 8 | 100 | 100 |
| 9 | 20 | 20 |
| 10 | 100 | 100 |
+----------+-------------+-------------+
-- 11.查询每门课程被选修的学生数
select cname,count(student_id) from course left join score on corse_id=course.cid group by score.corse_id;
mysql> select cname,count(student_id) from course left join score on corse_id=course.cid group by score.corse_id;
+----------+-------------------+
| cname | count(student_id) |
+----------+-------------------+
| 生物 | 1 |
| 体育 | 2 |
| 物理 | 1 |
| 英语 | 1 |
| 数学 | 1 |
| 科学 | 1 |
| 美术 | 1 |
| 思想品德 | 1 |
| 语文 | 1 |
| 地理 | 1 |
+----------+-------------------+
-- 12.查询姓“张”的学生名单；
select * from student where sname like '张%';
mysql> select * from student where sname like '张%';
+-----+--------+--------+----------+
| sid | sname | gender | class_id |
+-----+--------+--------+----------+
| 4 | 张全蛋 | 男 | 3 |
+-----+--------+--------+----------+
-- 13.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 corse_id,avg(number) from score right join course on corse_id = course.cid group by score.corse_id order by avg(number),course.cid desc ;
mysql> select corse_id,avg(number) from score right join course on corse_id = course.cid group by score.corse_id order by avg(number),course.cid desc ;
+----------+-------------+
| corse_id | avg(number) |
+----------+-------------+
| 9 | 20.0000 |
| 1 | 60.0000 |
| 5 | 70.0000 |
| 2 | 79.5000 |
| 7 | 80.0000 |
| 6 | 80.0000 |
| 3 | 80.0000 |
| 4 | 90.0000 |
| 10 | 100.0000 |
| 8 | 100.0000 |
+----------+-------------+
-- 14.查询平均成绩大于85的所有学生的学号、姓名和平均成绩
select student.sid,student.sname,avg(number) from student left join score on student.sid=student_id having avg(number) > 85;
-- 15.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 student.sid,student.sname from student left join score student.sid=student_id where corse_id =3 and number >80;
-- 16.查询各个课程及相应的选修人数
select course.cname,count(score.student_id) from course left join score on corse_id=course.cid group by course.cname;
+----------+-------------------------+
| cname | count(score.student_id) |
+----------+-------------------------+
| 体育 | 2 |
| 地理 | 1 |
| 思想品德 | 1 |
| 数学 | 1 |
| 物理 | 1 |
| 生物 | 1 |
| 科学 | 1 |
| 美术 | 1 |
| 英语 | 1 |
| 语文 | 1 |
+----------+-------------------------+
-- 17.查询“4”课程分数小于60，按分数降序排列的同学学号
select student.sid from student right join score on student.sid=student_id where corse_id = 4 and number <60 order by student.sid desc;
-- 18.删除学号为“2”的同学的“1”课程的成绩
delete from score where student_id =2 and corse_id =1;
# 班级
create table class(
cid int auto_increment primary key,
caption varchar(32) not null default ''
)charset utf8;
# 插入数据
insert into class(caption) values('三年二班'),('一年三班'),('三年一班');
# 学生
create table student(
sid int auto_increment primary key,
sname varchar(32) not null default '',
gender char(2) not null default '',
class_id int not null default 1,
constraint fk_cls_stu foreign key (class_id)references class(cid)
)charset utf8;
# 插入数据
insert into student(sname,gender,class_id) values ('钢蛋','女',1),('铁锤','女',1),('山炮','男',2);
# 老师
create table teacher(
tid int auto_increment primary key,
tname varchar(32) not null default ''
)charset utf8;
# 插入数据
insert into teacher(tname) values('波多'),('苍空'),('饭岛');
# 课程
create table course(
cid int auto_increment primary key,
cname varchar(32) not null default '',
teacher_id int not null default 1,
constraint fk_teacher_course foreign key (teacher_id) references teacher(tid)
)charset utf8;
# 插入数据
insert into course(cname,teacher_id)values('生物',1),('体育',1),('物理',2),('英语',3),('数学',4),('科学',4),('美术',6),('思想品德',7),('语文',5),('地理',8);
# 成绩
create table score(
sid int auto_increment primary key,
student_id int not null,
corse_id int not null,
number int not null,
constraint fk_stu_sco foreign key (student_id) references student(sid),
constraint fk_cor_sco foreign key (corse_id) references course(cid)
)charset utf8;
# 插入数据
insert into score(student_id,corse_id,number)values(1,1,60),(1,2,59),(2,2,100);