class表：
mysql> create table class(
-> cid int auto_increment primary key,
-> caption char(32) not null default ''
-> )charset utf8;
Query OK, 0 rows affected (0.03 sec)
mysql> insert into class(caption) values('三年二班'),('一年三班'),('三年一班');
Query OK, 3 rows affected (0.01 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from class;
+-----+----------+
| cid | caption |
+-----+----------+
| 1 | 三年二班 |
| 2 | 一年三班 |
| 3 | 三年一班 |
+-----+----------+
3 rows in set (0.00 sec)
student表:
mysql> create table student(
-> sid int auto_increment primary key,
-> sname char(20) not null default '',
-> gender enum('男','女') not null default '女',
-> class_id int not null default 1,
-> constraint fk_stu_class foreign key(class_id) references class(cid)
-> )charset utf8;
Query OK, 0 rows affected (0.03 sec)
mysql> insert into student(sname,gender,class_id) values('钢蛋','女',1),('铁锤','女',1),('山炮',
'男',2);
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from student;
+-----+-------+--------+----------+
| sid | sname | gender | class_id |
+-----+-------+--------+----------+
| 1 | 钢蛋 | 女 | 1 |
| 2 | 铁锤 | 女 | 1 |
| 3 | 山炮 | 男 | 2 |
+-----+-------+--------+----------+
3 rows in set (0.00 sec)
teacher表：
mysql> create table teacher(
-> tid int auto_increment primary key,
-> tname char(32) not null default ''
-> )charset utf8;
mysql> insert into teacher(tname) values('波多野结衣'),('苍井空'),('饭岛');
mysql> select * from teacher;
+-----+------------+
| tid | tname |
+-----+------------+
| 1 | 波多野结衣 |
| 2 | 苍井空 |
| 3 | 饭岛 |
+-----+------------+
3 rows in set (0.00 sec)
course表：
mysql> create table course(
-> cid int auto_increment primary key,
-> cname char(32) not null default '',
-> teacher_id int not null default 1,
-> constraint fk_cour_tea foreign key(teacher_id) references teacher(tid)
-> )charset utf8;
mysql> insert into course(cname,teacher_id) values('生物',1),('体育',1),('物理',2);
mysql> select * from course;
+-----+-------+------------+
| cid | cname | teacher_id |
+-----+-------+------------+
| 1 | 生物 | 1 |
| 2 | 体育 | 1 |
| 3 | 物理 | 2 |
+-----+-------+------------+
3 rows in set (0.00 sec)
score表：
mysql> create table score(
-> sid int auto_increment primary key,
-> student_id int not null default 1,
-> course_id int not null default 1,
-> number int not null default 1,
-> constraint fk_score_student foreign key (student_id) references student(si
d),
-> constraint fk_score_course foreign key (course_id) references course(cid)
-> )charset utf8;
mysql> insert into score(student_id,course_id，number) values (1,1,60),(1,2,59),(2,2,100);
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from score;
+-----+------------+-----------+--------+
| sid | student_id | course_id | number |
+-----+------------+-----------+--------+
| 1 | 1 | 1 | 60 |
| 2 | 1 | 2 | 59 |
| 3 | 2 | 2 | 100 |
+-----+------------+-----------+--------+
3 rows in set (0.00 sec)
1. 查询所有大于60分的学生的姓名和学号 (DISTINCT: 去重)
mysql> select sname,student.sid,number from student left join score on student.s
id=score.student_id where number>60;
+-------+-----+--------+
| sname | sid | number |
+-------+-----+--------+
| 铁锤 | 2 | 100 |
+-------+-----+--------+
1 row in set (0.00 sec)
-- 2.查询每个老师教授的课程数量 和 老师信息
mysql> select * from course left join teacher on teacher_id=teacher.
+-----+-------+------------+------+------------+
| cid | cname | teacher_id | tid | tname |
+-----+-------+------------+------+------------+
| 1 | 生物 | 1 | 1 | 波多野结衣 |
| 2 | 体育 | 1 | 1 | 波多野结衣 |
| 3 | 物理 | 2 | 2 | 苍井空 |
+-----+-------+------------+------+------------+
3 rows in set (0.00 sec)
-- 3. 查询学生的信息以及学生所在的班级信息
mysql> select * from student left join class on class_id=class.cid;
+-----+-------+--------+----------+------+----------+
| sid | sname | gender | class_id | cid | caption |
+-----+-------+--------+----------+------+----------+
| 1 | 钢蛋 | 女 | 1 | 1 | 三年二班 |
| 2 | 铁锤 | 女 | 1 | 1 | 三年二班 |
| 3 | 山炮 | 男 | 2 | 2 | 一年三班 |
+-----+-------+--------+----------+------+----------+
3 rows in set (0.00 sec)
-- 4、学生中男生的个数和女生的个数
mysql> select count(sid),gender from student group by gender;
+------------+--------+
| count(sid) | gender |
+------------+--------+
| 1 | 男 |
| 2 | 女 |
+------------+--------+
2 rows in set (0.00 sec)
-- 5、获取所有学习'生物'的学生的学号和成绩；姓名
mysql> select student.sid,sname,number,cname from student left join score on stu
dent.sid=score.student_id left join course on course.cid=score.course_id where c
name='生物';
+-----+-------+--------+-------+
| sid | sname | number | cname |
+-----+-------+--------+-------+
| 1 | 钢蛋 | 60 | 生物 |
+-----+-------+--------+-------+
1 row in set (0.00 sec)
-- 6、查询平均成绩大于60分的同学的学号和平均成绩；
mysql> select student_id,avg(number) from score group by student_id having avg(n
umber)>60;
+------------+-------------+
| student_id | avg(number) |
+------------+-------------+
| 2 | 100.0000 |
+------------+-------------+
1 row in set (0.00 sec)
-- 7、查询姓“李”的老师的个数；
mysql> insert into teacher(tname) values('李白'),('叶平');
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select count(tname) from teacher where tname='李白';
+--------------+
| count(tname) |
+--------------+
| 1 |
+--------------+
1 row in set (0.00 sec)
-- 8、查询课程成绩小于60分的同学的学号、姓名；
mysql> select sname,student.sid,number from student left join score on student.s
id=score.student_id where number<60;
+-------+-----+--------+
| sname | sid | number |
+-------+-----+--------+
| 钢蛋 | 1 | 59 |
+-------+-----+--------+
1 row in set (0.00 sec)
-- 9. 删除学习“叶平”老师课的SC表记录
mysql> insert into course(cname,teacher_id) values('语文',4);
Query OK, 1 row affected (0.00 sec)
mysql> select * from course;
+-----+-------+------------+
| cid | cname | teacher_id |
+-----+-------+------------+
| 1 | 生物 | 1 |
| 2 | 体育 | 1 |
| 3 | 物理 | 2 |
| 4 | 语文 | 4 |
+-----+-------+------------+
4 rows in set (0.00 sec)
mysql> delete from course where cid=4;
Query OK, 1 row affected (0.01 sec)
-- 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；
mysql> select course_id,max(number),min(number) from score group by c
+-----------+-------------+-------------+
| course_id | max(number) | min(number) |
+-----------+-------------+-------------+
| 1 | 60 | 60 |
| 2 | 100 | 59 |
+-----------+-------------+-------------+
2 rows in set (0.00 sec)
-- 11.查询每门课程被选修的学生数
-- 12.查询姓“张”的学生名单；
-- 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
-- 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
-- 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；
-- 16.查询各个课程及相应的选修人数
-- 17.查询“4”课程分数小于60，按分数降序排列的同学学号
-- 18.删除学号为“2”的同学的“1”课程的成绩