MySQL数据库的练习

蚂蚁小草

1,统计每个部门有多少人
1,select dept_no ,count(*)as dept_count,d_name from em join dept on em.dept_no=
dept.d_no group by dept_no;//第一种写法
select dept.d_name,dept_no,count(*) as dept_count from dept,em where dept.d_no=
em.dept_no group by dept_no;//第二种写法
+---------+------------+----------+
| dept_no | dept_count | d_name |
+---------+------------+----------+
| 10 | 2 | kuaiji |
| 20 | 3 | yanjiu |
| 30 | 4 | xiaoshou |
+---------+------------+----------+
2,查询每个部门平均薪水是多少
2,select dept_no ,avg(e_salary)as avg_salary,d_name from em join dept on em.dept_no=
dept.d_no group by dept_no;
select dept_no,avg(e_salary),d_name from em,dept where dept_no=d_no group by dept_no;
| dept_no | avg_salary | d_name |
+---------+------------+----------+
| 10 | 3725.0000 | kuaiji |
| 20 | 2358.3333 | yanjiu |
| 30 | 1637.5000 | xiaoshou |
+---------+------------+----------+
3,查询每个部们中薪水最高的员工的个人信息
3,select * from em where e_salary in(select max(e_salary) from em,dept where dept_no =
d_no group by d_name);
+------+--------+----------+---------+---------+----------+------------+
| e_no | e_name | e_gender | dept_no | e_job | e_salary | hireDate |
+------+--------+----------+---------+---------+----------+------------+
| 1006 | blake | f | 30 | manager | 2850 | 1997-02-15 |
| 1008 | scott | m | 20 | yanjiu | 3000 | 2003-05-12 |
| 1009 | king | f | 10 | zongcai | 5000 | 1995-01-01 |
+------+--------+----------+---------+---------+----------+------------+
4,查询在深圳工作的员工信息
4,select em.*,dept.d_location from em join dept on em.dept_no=
dept.d_no and dept.d_location='shenzhen';//第一种写法
select * from em where dept_no=(select d_no from dept where d_location='shenzhen');//第二种写法
结果1:
+------+--------+----------+---------+----------+----------+------------+------------+
| e_no | e_name | e_gender | dept_no | e_job | e_salary | hiredate | d_location |
+------+--------+----------+---------+----------+----------+------------+------------+
| 1005 | martin | m | 30 | salesman | 1250 | 2001-06-12 | shenzhen |
| 1006 | blake | f | 30 | manager | 2850 | 1997-02-15 | shenzhen |
| 1010 | turner | f | 30 | salesman | 1500 | 1997-10-12 | shenzhen |
+------+--------+----------+---------+----------+----------+------------+------------+
结果2:
+------+--------+----------+---------+----------+----------+------------+
| e_no | e_name | e_gender | dept_no | e_job | e_salary | hiredate |
+------+--------+----------+---------+----------+----------+------------+
| 1005 | martin | m | 30 | salesman | 1250 | 2001-06-12 |
| 1006 | blake | f | 30 | manager | 2850 | 1997-02-15 |
| 1010 | turner | f | 30 | salesman | 1500 | 1997-10-12 |
+------+--------+----------+---------+----------+----------+------------+

5,查询jones所在的部门和部门的地址信息
5,select dept.d_name,dept.d_location from dept join em on dept.d_no=
em.dept_no and em.e_name='james';//第一种写法
select dept.d_name,dept.d_location from dept left join em on dept.d_no=
em.dept_no and em.e_name='james';//第二种写法
select d_name,d_location from dept,em where d_no=dept_no and e_name='jones';//第三种方法
+--------+------------+
| d_name | d_location |
+--------+------------+
| yanjiu | beijing |
+--------+------------+

命令记录:

-链接数据库
mysql -h localhost -u root -p
或者(本机下的数据库)
mysql -u root -p

1.显示服务器上的所有数据库
show databases;

-创建数据库
create database database_name;
-查看数据库的定义信息
show create database database_name;
-删除数据库
drop database database_name;

------------表的操作-----------

-选中数据库
use database_name;
-创建数据表
create table table_name(
id int(11),
name varchar(11)
)
-查看数据库中的所有表
show tables;
-查看表的定义信息
show create table table_name\G;
-查看表的基本信息结构
describe table_name;
-设置表的主键
1. create table tb_emp2(id int(11)primary key,name varchar(25),deptld int(11),salary float);

2. create table tb_emp3(id int(11),name varchar(25),deptld int(11),salary float,primary key(id));

3.create table tb_emp4(name varchar(25),deptld int(11),salary float,primary key(name,deptld));

-设置外键
表一:
create table tb_dept1(id int(11)primary key,name varchar(22) not null,location varchar(50));
表二:
create table tb_emp5(id int(11)primary key,name varchar(25),deptld int(11),salary float,constraint fk_emp_dept1 foreign key(deptid) references tb_dept1(id));

-非空约束
字段名数据类型 NOT NULL,
-唯一性约束
(1)字段名数据类型 UNIQUE,
(2)[constraint <约束名>]UNIQUE(name)
-默认约束
字段名数据类型 default 默认值
deptid int(11)default 1111,
-设置表的属性值自动增加
字段名数据类型 auto_increment
id int(11) primary key auto_increment,
-- -- -- -- -- -- --改变表-- -- --alter-- -- --
-修改表名
alter table <旧表名> rename [to] <新表名>;
alter table tb_dept3 rename tb_deptment3;
-修改字段的数据类型
alter table <表名> modify <字段名> <数据类型>
alter table tb_dept1 modify name varchar(30) --将name的varchar(22)改为(30)
-修改字段名
alter table <表名>change<旧字段名><新字段名><新数据类型>
alter table tb_dept1 change location loc varchar(50),--将location改为loc,其他不变;也可以改变varchar(50)为其他的数字
-添加字段
alter table <表名>add<新字段名><数据类型>[约束条件][first|after 已存在的字段名];
(1)alter table tb_dept1 add managerld int(10);
(2)alter table tb_dept1 add columnl varchar(12) not null;
(3)alter table tb_dept1 add column2 int(11) first;
(4)alter table tb_dept1 add column3 int(11) after name;
-删除字段
alter table <表名>drop<字段名>
alter table tb_dept1 drop column2;
-修改字段排列位置
alter table<表名>modify<字段1><数据类型>first|after<字段2>
alter table tb_dept1 modify column3 varchar(12)first;
alter table tb_dept1 modify columnl varchar(12) after location;
-删除外键约束
alter table <表名>drop foreign key <外键约束名>
alter table tb_dept3 drop foreign key fk_emp_dept1;
----------------------数据处理-(student 为表名)---------------------
-插入数据
insert into 表名 values(内容);
insert into student values(101,'张三', '男',1985,'计算机系', '北京市海淀区');
- 查询表中所有数据
select * from student;
select * from 表名;
- 查询表中的2-4条记录
select * from student limit 1,3;
- 从student表查询所有学生的学号（id）、姓名（name）和院系（department）的信息
SELECT id,name,department FROM student;
- 从student表中查询计算机系和英语系的学生的信息
SELECT * FROM student WHERE department IN ('计算机系','英语系');
- 从student表中查询年龄18~22岁的学生信息
SELECT id,name,sex,2013-birth AS age,department,address FROM student WHERE 2013-birth BETWEEN 18 AND 22;
- 从student表中查询每个院系有多少人
SELECT department, COUNT(id) FROM student GROUP BY department;
- 从score表中查询每个科目的最高分
SELECT c_name,MAX(grade) FROM score GROUP BY c_name;
- 查询李四的考试科目（c_name）和考试成绩（grade）
SELECT c_name, grade FROM score WHERE stu_id= (SELECT id FROM student WHERE name= '李四' );
- 用连接的方式查询所有学生的信息和考试信息
SELECT student.id,name,sex,birth,department,address,c_name,grade FROM student,score WHERE student.id=score.stu_id;
- 计算每个学生的总成绩
SELECT student.id,name,SUM(grade) FROM student,score WHERE student.id=score.stu_id GROUP BY id;
- 计算每个考试科目的平均成绩
SELECT c_name,AVG(grade) FROM score GROUP BY c_name;
- 查询计算机成绩低于95的学生信息
SELECT * FROM student WHERE id IN (SELECT stu_id FROM score WHERE c_name="计算机" and grade<95);
- 查询一组数据的平均值的最大值
select s_id,avg(f_price) as a_price from fruits group by s_id order by a_price desc limit 1;
- 查询同时参加计算机和英语考试的学生的信息
SELECT * FROM student WHERE id =ANY ( SELECT stu_id FROM score WHERE stu_id IN (SELECT stu_id FROM score WHERE c_name= '计算机') AND c_name= '英语' );
- 将计算机考试成绩按从高到低进行排序
SELECT stu_id, grade FROM score WHERE c_name= '计算机' ORDER BY grade DESC;
- 从student表和score表中查询出学生的学号，然后合并查询结果
SELECT id FROM student UNION SELECT stu_id FROM score;
- 查询姓张或者姓王的同学的姓名、院系和考试科目及成绩
SELECT student.id, name,sex,birth,department, address, c_name,grade FROM student, score WHERE (name LIKE '张%' OR name LIKE '王%') AND student.id=score.stu_id ;
- 查询都是湖南的学生的姓名、年龄、院系和考试科目及成绩
SELECT student.id, name,sex,birth,department, address, c_name,grade FROM student, score WHERE address LIKE '湖南%' AND student.id=score.stu_id;

数据表的操作练习:
http://blog.sina.com.cn/s/blog_767d65530101861c.html

MySQL数据库的练习

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