一、表关系
二、创建数据库和表
（一）创建数据库
创建数据库test2，用于存放上述表
mysql> create database test2 default charset utf8 collate utf8_general_ci; Query OK, 1 row affected (0.00 sec)
（二）创建表
创建上述表以及相应的约束
- 创建班级表
mysql> create table class (
-> cid int primary key auto_increment comment '主键ID' ,
-> caption varchar(64) not null comment '班级名称'
-> )charset=utf8 collate=utf8_general_ci engine=innodb comment='班级表
Query OK, 0 rows affected (0.02 sec)
mysql> show tables;
+-----------------+
| Tables_in_test2 |
+-----------------+
| class |
+-----------------+
1 row in set (0.00 sec)
mysql> desc class;
+---------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+----------------+
| cid | int(11) | NO | PRI | NULL | auto_increment |
| caption | varchar(64) | NO | | NULL | |
+---------+-------------+------+-----+---------+----------------+
2 rows in set (0.01 sec)
- 创建学生表
mysql> create table student(
-> sid int primary key auto_increment comment '主键ID',
-> sname varchar(32) not null comment '学生名字',
-> gender enum('男','女') not null default '男' comment '性别',
-> class_id int comment '关联班级外键',
-> constraint fk_student_class foreign key(class_id) references class(cid)
-> )charset=utf8 collate=utf8_general_ci engine=innodb comment '学生表';
Query OK, 0 rows affected (0.03 sec)
mysql> show tables;
+-----------------+
| Tables_in_test2 |
+-----------------+
| class |
| student |
+-----------------+
2 rows in set (0.00 sec)
mysql> desc student;
+----------+-----------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-----------------+------+-----+---------+----------------+
| sid | int(11) | NO | PRI | NULL | auto_increment |
| sname | varchar(32) | NO | | NULL | |
| gender | enum('男','女') | NO | | 男 | |
| class_id | int(11) | YES | MUL | NULL | |
+----------+-----------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)
- 创建教师表
mysql> create table teacher(
-> tid int primary key auto_increment comment '主键ID',
-> tname varchar(32) comment '老师名字'
-> )charset=utf8 collate=utf8_general_ci engine=innodb comment='教师表';
Query OK, 0 rows affected (0.02 sec)
mysql> desc teacher;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| tid | int(11) | NO | PRI | NULL | auto_increment |
| tname | varchar(32) | YES | | NULL | |
+-------+-------------+------+-----+---------+----------------+
2 rows in set (0.01 sec)
- 创建课程表
mysql> create table course(
-> cid int primary key auto_increment comment '课程表',
-> cname varchar(32) comment '课程名称',
-> unique index_cname(cname),
-> teacher_id int comment '关联教师表的外键',
-> constraint fk_course_teacher foreign key(teacher_id) references teacher(t
id)
-> )charset=utf8 collate=utf8_general_ci engine=innodb comment='课程表';
Query OK, 0 rows affected (0.03 sec)
mysql> desc course;
+------------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+-------------+------+-----+---------+----------------+
| cid | int(11) | NO | PRI | NULL | auto_increment |
| cname | varchar(32) | YES | UNI | NULL | |
| teacher_id | int(11) | YES | MUL | NULL | |
+------------+-------------+------+-----+---------+----------------+
3 rows in set (0.01 sec)
- 创建成绩表
mysql> create table score(
-> sid int primary key auto_increment comment '成绩表',
-> student_id int comment '添加关联学生表的外键字段',
-> constraint fk_score_student foreign key(student_id) references student(sid),
-> course_id int comment '添加关联课程表的外键字段',
-> constraint fk_score_course foreign key(course_id) references course(cid),
-> unique index_together(student_id,course_id) comment '将学生和成绩进行联合唯一索引',
-> number float(255,2) comment '学生成绩'
-> )charset=utf8 collate=utf8_general_ci engine=innodb comment='成绩表';
Query OK, 0 rows affected (0.03 sec)
mysql> desc score;
+------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+--------------+------+-----+---------+----------------+
| sid | int(11) | NO | PRI | NULL | auto_increment |
| student_id | int(11) | YES | MUL | NULL | |
| course_id | int(11) | YES | MUL | NULL | |
| number | float(255,2) | YES | | NULL | |
+------------+--------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)
三、创建测试数据
- 班级表添加数据
mysql> insert into class(caption)values('三年二班'),('一年三班'),('三年一班');
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
- 学生表添加数据
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
- 教师表添加数据
mysql> insert into teacher(tname) values('波多'),('苍空'),('饭岛');
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
- 课程表添加数据
mysql> insert into course(cname,teacher_id) values('生物',1),('体育',1),('物理',2);
Query OK, 3 rows affected (0.00 sec)
Records: 3 Duplicates: 0 Warnings: 0
- 成绩表添加数据
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
四、操作数据表
1、查询“生物”课程比“物理”课程成绩高的所有学生的学号
分析：先查出所有生物课程成绩的学生；其次查出所有物理课程成绩的学生；最后将上述两个结果进行相连通过where语句查出符合要求的学生
#查出生物相关成绩的学生
mysql> select s.student_id,c.cname,s.number from course c left join score s on c
.cid=s.course_id where c.cname='生物';
+------------+-------+--------+
| student_id | cname | number |
+------------+-------+--------+
| 1 | 生物 | 60.00 |
+------------+-------+--------+
1 row in set (0.00 sec)
#查出物理成绩相关学生
mysql> select s.student_id,c.cname,s.number from course c left join score s on c
.cid=s.course_id where c.cname='物理';
+------------+-------+--------+
| student_id | cname | number |
+------------+-------+--------+
| NULL | 物理 | NULL |
+------------+-------+--------+
1 row in set (0.00 sec)
#查出符合条件的结果
mysql> select d.student_id,d.cname,d.number from (select s.student_id,c.cname,s
.number from course c left join score s on c.cid=s.course_id where c.cname='生物')as d
-> left join (select s.student_id,c.cname,s.number from course c left join score s on c.cid=s.course_id where c.cname='物理') as e on d.student_id=e.student
_id where
-> d.number > ifnull(e.number,0);
+------------+-------+--------+
| student_id | cname | number |
+------------+-------+--------+
| 1 | 生物 | 60.00 |
+------------+-------+--------+
1 row in set (0.01 sec)
mysql>
2、查询平均成绩大于60分的同学的学号和平均成绩
分析：
- 先查出所有同学的学号、各科成绩；
- 其次是分组，根据学生的学号进行分组；
- 计算出每一个学生的平均成绩；
- 平均成绩大于60分的筛选出来；
#查出所有学生的学号和各科目的成绩 mysql> select sc.student_id,sc.course_id,number from student st left join score sc on st.sid = sc.student_id; +------------+-----------+--------+ | student_id | course_id | number | +------------+-----------+--------+ | 1 | 1 | 60.00 | | 1 | 2 | 59.00 | | 2 | 2 | 100.00 | | NULL | NULL | NULL | +------------+-----------+--------+ 4 rows in set (0.00 sec) #进行分组 mysql> select sc.student_id,sc.course_id,number from student st left join score sc on st.sid = sc.student_id group by sc.student_id; +------------+-----------+--------+ | student_id | course_id | number | +------------+-----------+--------+ | NULL | NULL | NULL | | 1 | 1 | 60.00 | | 2 | 2 | 100.00 | +------------+-----------+--------+ #计算每一个学生的平均成绩 mysql> select sc.student_id,sc.course_id,number,avg(number) from student st left join score sc on st.sid = sc.student_id group by sc.student_id; +------------+-----------+--------+-------------+ | student_id | course_id | number | avg(number) | +------------+-----------+--------+-------------+ | NULL | NULL | NULL | NULL | | 1 | 1 | 60.00 | 59.500000 | | 2 | 2 | 100.00 | 100.000000 | +------------+-----------+--------+-------------+ 3 rows in set (0.00 sec) #筛选出最后的结果 mysql> select sc.student_id,sc.course_id,number,avg(number) as stu_avg from stud ent st left join score sc on st.sid = sc.student_id group by sc.student_id havin g stu_avg > 60; +------------+-----------+--------+------------+ | student_id | course_id | number | stu_avg | +------------+-----------+--------+------------+ | 2 | 2 | 100.00 | 100.000000 | +------------+-----------+--------+------------+ 1 row in set (0.00 sec)
3、查询所有同学的学号、姓名、选课数、总成绩
分析：
- 查询所有的学生信息
- 在进行统计选课数、总成绩时是针对每一个学生，所以必须以学生学号进行分组
- 统计出最后的结果
mysql> select sc.student_id,st.sname,count(sc.course_id),sum(number) from studen t st left join score sc on st.sid = sc.student_id group by sc.student_id; +------------+-------+---------------------+-------------+ | student_id | sname | count(sc.course_id) | sum(number) | +------------+-------+---------------------+-------------+ | NULL | 山炮 | 0 | NULL | | 1 | 钢蛋 | 2 | 119.00 | | 2 | 铁锤 | 1 | 100.00 | +------------+-------+---------------------+-------------+ 3 rows in set (0.00 sec)
4、查询姓“李”的老师的个数
#使用正则表达式 mysql> select * from teacher where tname regexp '^李'; Empty set (0.00 sec)
5、查询没学过“叶平”老师课的同学的学号、姓名
分析：
- 通过成绩表与学生表、课程表获取学生、课程以及教师id信息
- 将上述查出的结果与教师表连表获取最终结果
#获取学生、课程教师id信息 mysql> select sc.student_id,st.sname,co.cname,co.teacher_id from score sc left j oin student st on st.sid = sc.student_id left join course co on co.cid = sc.cour se_id; +------------+-------+-------+------------+ | student_id | sname | cname | teacher_id | +------------+-------+-------+------------+ | 1 | 钢蛋 | 生物 | 1 | | 1 | 钢蛋 | 体育 | 1 | | 2 | 铁锤 | 体育 | 1 | +------------+-------+-------+------------+ 3 rows in set (0.00 sec) #获取最终结果 mysql> select a.student_id,a.sname from (select sc.student_id,st.sname,co.cname, co.teacher_id from score sc left join student st on st.sid = sc.student_id left join course co on co.cid = sc.course_id) as a left join teacher te on a.teacher_ id=te.tid where te.tname != '叶平'; +------------+-------+ | student_id | sname | +------------+-------+ | 1 | 钢蛋 | | 1 | 钢蛋 | | 2 | 铁锤 | +------------+-------+ 3 rows in set (0.00 sec)
6、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名
分析：
- 先查出学习001课程所有的学生信息
- 再查出学习002课程所有学生的信息
- 上面查出的结果再作为查询结果集，查出符合条件的结果，条件就是这两个课程的学生id是一样的
#所有学生的信息
mysql> select st.sid,st.sname,co.cid,co.cname from score sc left join student st
-> on sc.student_id = st.sid left join course co on sc.course_id = co.cid;
+------+-------+------+-------+
| sid | sname | cid | cname |
+------+-------+------+-------+
| 1 | 钢蛋 | 1 | 生物 |
| 1 | 钢蛋 | 2 | 体育 |
| 2 | 铁锤 | 2 | 体育 |
+------+-------+------+-------+
3 rows in set (0.00 sec)
#001课程学生信息
mysql> select b.sid,b.sname from
-> (select a.sid,a.sname,a.cid,a.cname from (select st.sid,st.sname,co.cid,co.cname from score sc left join student st
-> on sc.student_id = st.sid left join course co on sc.course_id = co.cid)as a where a.cid=2) as b;
+------+-------+
| sid | sname |
+------+-------+
| 2 | 铁锤 |
| 1 | 钢蛋 |
+------+-------+
2 rows in set (0.00 sec)
#002课程学生信息
mysql> select c.sid,c.sname from (select a.sid,a.sname,a.cid,a.cname from (select st.sid,st.sname,co.cid,co.cname from score sc left join student st
-> on sc.student_id = st.sid left join course co on sc.course_id = co.cid)
as a where a.cid=1) as c;
+------+-------+
| sid | sname |
+------+-------+
| 1 | 钢蛋 |
+------+-------+
1 row in set (0.00 sec)
#利用同一个学生作为条件进行查询
mysql> select b.sid,b.sname from
-> (select a.sid,a.sname,a.cid,a.cname from (select st.sid,st.sname,co.cid,co.cname from score sc left join student st
-> on sc.student_id = st.sid left join course co on sc.course_id = co.cid)as a where a.cid=2) as b,
->
-> (select a.sid,a.sname,a.cid,a.cname from (select st.sid,st.sname,co.cid,co.cname from score sc left join student st
-> on sc.student_id = st.sid left join course co on sc.course_id = co.cid)as a where a.cid=1) as c
->
-> where b.sid = c.sid;
+------+-------+
| sid | sname |
+------+-------+
| 1 | 钢蛋 |
+------+-------+
1 row in set (0.00 sec)
7、查询学过“叶平”老师所教的所有课的同学的学号、姓名
分析：
- 通过连表查出所有学生、教师、课程相关信息
- 进行过滤
#获取所有信息 mysql> select st.sid,st.sname,te.tname,co.cname from score sc left join course c o on sc.course_id = co.cid left join teacher te on co.teacher_id = te.tid left j oin student st on sc.student_id = st.sid; +------+-------+-------+-------+ | sid | sname | tname | cname | +------+-------+-------+-------+ | 1 | 钢蛋 | 波多 | 生物 | | 1 | 钢蛋 | 波多 | 体育 | | 2 | 铁锤 | 波多 | 体育 | +------+-------+-------+-------+ 3 rows in set (0.00 sec) #过滤获取符合要求的结果 mysql> select st.sid,st.sname,te.tname,co.cname from score sc left join course c o on sc.course_id = co.cid left join teacher te on co.teacher_id = te.tid left j oin student st on sc.student_id = st.sid where te.tname='叶平'; Empty set (0.00 sec)
8、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名
分析：
- 查出课程编号“002”成绩的所有同学信息
- 查出课程编号“001”成绩的所有同学信息
- 通过where语句进行筛选（条件是同一个同学、002成绩小于001成绩）
#001成绩的同学信息
mysql> select st.sid,st.sname,sc.number from score sc left join course co on sc.
course_id = co.cid left join student st on sc.student_id = st.sid where co.cid=1
;
+------+-------+--------+
| sid | sname | number |
+------+-------+--------+
| 1 | 钢蛋 | 60.00 |
+------+-------+--------+
1 row in set (0.00 sec)
#002成绩的同学信息
mysql> select st.sid,st.sname,sc.number from score sc left join course co on sc.
course_id = co.cid left join student st on sc.student_id = st.sid where co.cid=2
;
+------+-------+--------+
| sid | sname | number |
+------+-------+--------+
| 1 | 钢蛋 | 59.00 |
| 2 | 铁锤 | 100.00 |
+------+-------+--------+
2 rows in set (0.00 sec)
#过滤条件
mysql> select a.sid,a.sname,a.number
-> from
-> (select st.sid,st.sname,sc.number from score sc left join course co on sc
.
-> course_id = co.cid left join student st on sc.student_id = st.sid where c
o.cid=1) as a,
->
-> (select st.sid,st.sname,sc.number from score sc left join course co on sc
.
-> course_id = co.cid left join student st on sc.student_id = st.sid where c
o.cid=2) as b
->
-> where a.sid = b.sid and a.number > b.number;
+------+-------+--------+
| sid | sname | number |
+------+-------+--------+
| 1 | 钢蛋 | 60.00 |
+------+-------+--------+
1 row in set (0.00 sec)
9、查询有课程成绩小于60分的同学的学号、姓名
分析：
- 通过连表获取所有同学的学号、姓名、课程、成绩信息
- 通过where过滤出符合条件的信息
#所有学生及成绩信息 mysql> select st.sid,st.sname,co.cname,sc.number from score sc left join student st on sc.student_id = st.sid left join course co on sc. course_id = co.cid; +------+-------+-------+--------+ | sid | sname | cname | number | +------+-------+-------+--------+ | 1 | 钢蛋 | 生物 | 60.00 | | 1 | 钢蛋 | 体育 | 59.00 | | 2 | 铁锤 | 体育 | 100.00 | +------+-------+-------+--------+ 3 rows in set (0.00 sec) #过滤 mysql> select st.sid,st.sname,co.cname,sc.number from score sc left join student st on sc.student_id = st.sid left join course co on sc. course_id = co.cid wher e number < 60; +------+-------+-------+--------+ | sid | sname | cname | number | +------+-------+-------+--------+ | 1 | 钢蛋 | 体育 | 59.00 | +------+-------+-------+--------+ 1 row in set (0.00 sec)
10、查询没有学全所有课的同学的学号、姓名
分析：
- 通过课程表计算出所有课程的数目(count)
- 计算出每一个同学(group by)所拥有的课程数量(count)
- 将上述结果作为结果集使用where过滤
#所有课程数量
mysql> select count(co.cid) as co_count from course co;
+----------+
| co_count |
+----------+
| 3 |
+----------+
1 row in set (0.00 sec)
#每一个同学拥有的课程数量
mysql> select st.sid,st.sname,count(co.cid) as st_co_count from score sc left jo
in student st on sc.student_id = st.sid left join course co on sc.course_id = co
.cid group by st.sid;
+------+-------+-------------+
| sid | sname | st_co_count |
+------+-------+-------------+
| 1 | 钢蛋 | 2 |
| 2 | 铁锤 | 1 |
+------+-------+-------------+
2 rows in set (0.00 sec)
#进行过滤
mysql> select a.sid,a.sname,a.st_co_count from (select st.sid,st.sname,count(co.
cid) as st_co_count from score sc left join student st on sc.student_id = st.sid
left join course co on sc.course_id = co.cid group by st.sid) as a,
-> (select count(co.cid) as co_count from course co) as b
-> where a.st_co_count < b.co_count;
+------+-------+-------------+
| sid | sname | st_co_count |
+------+-------+-------------+
| 1 | 钢蛋 | 2 |
| 2 | 铁锤 | 1 |
+------+-------+-------------+
2 rows in set (0.00 sec)
11、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
分析：
- 查找“001”的同学的所有课程信息
- 查找除“001”“同学以外的同学所有课程的信息
- 通过课程名称进行过滤
#所有同学的所有课程信息
mysql> select st.sid,st.sname,co.cname from score sc left join student st on st.
sid = sc.student_id left join course co on sc.course_id = co.cid;
+------+-------+-------+
| sid | sname | cname |
+------+-------+-------+
| 1 | 钢蛋 | 生物 |
| 1 | 钢蛋 | 体育 |
| 2 | 铁锤 | 体育 |
+------+-------+-------+
3 rows in set (0.00 sec)
#001同学课程的所有信息
mysql> select st.sid,st.sname,co.cname from score sc left join student st on st.
sid = sc.student_id left join course co on sc.course_id = co.cid where st.sid=1;
+-----+-------+-------+
| sid | sname | cname |
+-----+-------+-------+
| 1 | 钢蛋 | 生物 |
| 1 | 钢蛋 | 体育 |
+-----+-------+-------+
2 rows in set (0.00 sec)
#除001同学以外的同学课程信息
mysql> select st.sid,st.sname,co.cname from score sc left join student st on st.
sid = sc.student_id left join course co on sc.course_id = co.cid where st.sid !=
1;
+------+-------+-------+
| sid | sname | cname |
+------+-------+-------+
| 2 | 铁锤 | 体育 |
+------+-------+-------+
1 row in set (0.00 sec)
#通过课程名字进行过滤
mysql> select a.sid,a.sname,a.cname from
-> (select st.sid,st.sname,co.cname from score sc left join student st on st
.
-> sid = sc.student_id left join course co on sc.course_id = co.cid where st
.sid = 1) as a,
-> (select st.sid,st.sname,co.cname from score sc left join student st on st
.
-> sid = sc.student_id left join course co on sc.course_id = co.cid where st
.sid != 1) as b
-> where b.cname regexp a.cname;
+------+-------+-------+
| sid | sname | cname |
+------+-------+-------+
| 1 | 钢蛋 | 体育 |
+------+-------+-------+
1 row in set (0.00 sec)
12、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
分析：
这个和上面的差不多，只不过在最后的筛选条件处做一些改变
mysql> select a.sid,a.sname,a.cname from
-> (select st.sid,st.sname,co.cname from score sc left join student st on st
.
-> sid = sc.student_id left join course co on sc.course_id = co.cid where st
.sid != 2) as a,
-> (select st.sid,st.sname,co.cname from score sc left join student st on st
.
-> sid = sc.student_id left join course co on sc.course_id = co.cid where st
.sid = 2) as b
-> where b.cname = a.cname;
+------+-------+-------+
| sid | sname | cname |
+------+-------+-------+
| 1 | 钢蛋 | 体育 |
+------+-------+-------+
1 row in set (0.00 sec)
13、删除学习“叶平”老师课的SC表记录
分析：
- 先查找出叶平老师所教课程的所有cid
- 根据课程cid删除对应的记录
#叶平老师所教课程的cid mysql> select co.cid from course co left join teacher te on co.teacher_id=te.tid where te.tname='叶平'; Empty set (0.00 sec) #根据cid删除记录 mysql> delete from score where course_id in (select co.cid from course co left join teacher te on co.teacher_id=te.tid where te.tname='叶平'); Query OK, 0 rows affected (0.00 sec)
......待续