mysql数据库练习第二章----二表查询

1.分别创建class表和stuent表

class表

student表

mysql> create table class (class_id int primary key auto_increment,class_name char(20),teacher char(20)) charset=utf8;

mysql> create table student(sid int primary key auto_increment,sname char(20),sage int,ssex enum('男','女'),hometown char(20),height float,class_id int,foreign key (class_id) references class(class_id)) charset=utf8;

2.插入数据

mysql> insert into class values(1,'一班','张三');

mysql> insert into class values(2,'二班','李四');

mysql> insert into class values(0,'三班','李四');

mysql> insert into class values(0,'四班','王五');

mysql> insert into class values(0,'五班','赵柳');

mysql> insert into class values(null,'六班','孙悟空');

mysql> insert into student values(0,'王子云',23,'2','河北',162,2);

mysql> insert into student values(0,'印小天',20,'1','天津',177,3);

mysql> insert into student values(0,'张无忌',25,'1','河南',176,4);

mysql> insert into student values(0,'赵敏',22,'2','广西',166,5);

mysql> insert into student values(0,'周芷若',23,'2','天津',162,6);

mysql> insert into student values(0,'​​张若昀​​​',22,'1','河北',176,1),(0,'​​范闲​​​',21,'1','北京',170,2),(0,'​​李沁​​​',18,'2','北京',160,3),(0,'​​林婉儿​​​',18,'2','北京',160,4),(0,'​​宋轶​​​',19,'2','天津',166,5),(0,'​​范若若​​',18,'2','河北',166,6);

mysql> insert into student values(0,'​​海棠朵朵​​​',18,'2','河北',167,1),(0,'​​辛芷蕾​​​',24,'2','北京',166,2),(0,'​​陈道明​​',25,'1','北京',178,3),(0,'​​庆帝​​​',25,'1','北京',180,4),(0,'​​吴刚​​​',20,'1','河南',172,5),(0,'​​陈萍萍​​',24,'1','河南',177,6);

mysql> insert into student values(0,'​​司理理​​​',17,'2','河北',167,1),(0,'​​李纯​​',24,'2','北京',166,2),(0,'​​叶灵儿​​',22,'2','广西',158,3),(0,'​​韩玖诺​​​',22,'1','北京',170,4),(0,'​​吴刚​​​',22,'1','河南',173,5),(0,'​​刘美彤​​',22,'2','天津',167,6);

3.数据库练习

3.1查询年龄18-22岁学生的信息。

3.2查询范闲的学号和班主任姓名

3.3计算每个老师学生的数量

3.4查询学生数量高于5人的老师的姓名和班级

3.5查询姓张或者姓李同学的身高，班主任姓名。

3.6查询来自河北的学生的全部信息

3.7查询来自河北学生的平均身高

3.8查询身高最高同学的老师的姓名

3.9查询学生平均身高高于170老师的姓名。

3.10删除一班身高最高学生的信息

3.11 修改学生sid 17的姓名为“张三丰”

3.12删除外键，重新添加。删除主键，重新添加。

3.1查询年龄18-22岁学生的信息。

select * from student,class where student.class_id=class.class_id and sage<=22 and sage>=18;

select * from student,class where student.class_id=class.class_id and sage between 18 and 22;

3.2查询范闲的学号和班主任姓名

select sid,sname,teacher from student,class where student.class_id=class.class_id and sname='范闲';

3.3计算每个老师学生的数量

select count(sname),teacher from class,student where student.class_id=class.class_id group by teacher;

3.4查询学生数量高于5人的老师的姓名和班级

select teacher,count(sname) from student,class where student.class_id=class.class_id group by teacher having count(*)>4;

select teacher,count(sname) from student,class where student.class_id=class.class_id group by teacher having count(sname)>4;

3.5查询姓张或者姓李同学的身高，班主任姓名。

 select sname,height,teacher from class,student where class.class_id=student.class_id and (sname like "张%" or sname like "李%");

3.6查询来自河北的学生的全部信息

select * from student,class where student.class_id=class.class_id and hometown='河北';

3.7查询来自河北学生的平均身高

select avg(height),hometown from class,student where class.class_id=student.class_id and hometown='河北';

3.8查询身高最高同学的老师的姓名

select * from student,class where student.class_id=class.class_id and height=(select max(height) from student);

3.9查询学生平均身高高于170老师的姓名。

select teacher,avg(height) from student,class where student.class_id=class.class_id group by teacher having avg(height)>170;

3.10删除一班身高最高学生的信息

3.11 修改学生sid 17的姓名为“张三丰”

update student set sname='张三丰' where sid=17;

3.12删除外键，重新添加。删除主键，重新添加。

删除外键，查看创建表student的命令。

show create table student;

删除外键： alter table student drop foreign key (class_id) references class(class_id);

重新添加外键：

alter table student add foreign key (class_id) references class (class_id);