mysql基本功能

SQL structed query language

连接MYSQL服务器：mysql -uroot -proot

数据库的操作：创建，查看，修改，删除

*创建：

创建一个名称为mydb1的数据库。

create
database mydb1;

创建一个使用utf-8字符集的mydb2数据库。

create
database mydb2 character set utf8;

创建一个使用utf-8字符集，并带校对规则的mydb3数据库。

create
database mydb2 character set utf8 collate utf8_general_ci;

*查看:

显示所有数据库

show
databases;

显示创建数据库的语句信息

show create
database mydb2;

*修改:

修改mydb1的字符集为gbk(不能修改数据库名)

alter
database mydb1 character set utf8;

*删除:

删除数据库mydb2

drop database
mydb1;

表的操作：创建，查看，修改，删除

*创建：

根据实体类Person创建表person

Person
{

int
id;

String
name;

}

create table
person(

id
int,

name
varchar(20)

);

mysql中的数据类型：

bit
1位　但可以指定位数，如：bit<3>

int 2字节
可以指定最大位数，如：int<4>　最大为4位的整数

float
2个字节　可以指定最大的位数和最大的小数位数，如：float<5,2> 最大为一个５位的数，小数位最多2位

double　4个字节　可以指定最大的位数和最大的小数位数，如：float<6,4>
最大为一个6位的数，小数位最多4位

char　必须指定字符数,如char(5)
为不可变字符　即使存储的内容为'ab',也是用5个字符的空间存储这个数据

varchar　必须指定字符数,如varchar(5)
为可变字符　如果存储的内容为'ab',占用2个字符的空间；如果为'abc',则占用3个字符的空间

text:
大文本(大字符串)

blob：二进制大数据　如图片，音频文件，视频文件

date:
日期　如：'1921-01-02'

datetime:
日期时间　如：'1921-01-02 12:23:43'

timeStamp:
时间戳，自动赋值为当前日期时间

创建一个员工表

create table
employee(

id
int,

name
varchar(20),

sex
bit,

birthday
date,

entry_date
date,

job
varchar(20),

salary
double,

resume
text

);

*查看：

查看所有的表：

show
tables;

查看指定表的创建语句

show create
table employee;

显示指定表的结构：

desc
employee;

*删除：

删除employee表

drop table employee;

*修改表：

增加一个字段：alter table worker add
column height double;

修改一个字段：alter table worker
modify column height float;

删除一个字段：alter table worker drop
column height;

更改表名：rename table employee to
worker;

修改表的字符集:alter table worker
character set gbk;

表数据的CRUD

*C(create增加数据) Insert语句

新建Employee表并表中添加一些记录

create table
employee(

id
int,

name
varchar(20),

sex
bit,

birthday
date,

salary
double,

entry_date
date,

resume
text

);

insert into
employee(name,id,sex,birthday,salary,entry_date,resume)
values('张三',1,1,'1983-09-21',15000,'2012-06-24','一个大牛');

insert into
employee(id,name,sex,birthday,salary,entry_date,resume)
values(2,'李四',1,'1984-09-21',10000,'2012-07-24','一个中牛');

insert into
employee(id,name,sex,birthday,salary,entry_date,resume)
values(3,'王五',0,'1985-09-21',7000,'2012-08-24','一个小牛');

*U(update更新数据) Update语句

将所有员工薪水都增加500元。

update
employee set salary=salary+500;

将王五的员工薪水修改为10000元，resume改为也是一个中牛

update
employee set salary=10000,resume='也是一个中牛' where name='王五';

*D(drop删除数据) Delete语句

删除表中姓名为王五的记录。

delete from
employee where name='王五';

删除表中所有记录。

delete from
employee; --可以有条件，但删除所有记录差了一点

使用truncate删除表中记录。

truncate
employee;--无条件 效率高

*R(Retrieve查找数据) Select语句

准备环境：

create table
student(

id
int,

name
varchar(20),

chinese
int,

english
int,

math
int

);

insert
into student(id,name,chinese,english,math)
values(1,'何东',80,85,90);

insert into
student(id,name,chinese,english,math)
values(2,'权筝',90,95,95);

insert into
student(id,name,chinese,english,math)
values(3,'何南',80,96,96);

insert into
student(id,name,chinese,english,math)
values(4,'叶坦',81,97,85);

insert into
student(id,name,chinese,english,math)
values(5,'何西',85,84,90);

insert into
student(id,name,chinese,english,math)
values(6,'丁香',92,85,87);

insert into
student(id,name,chinese,english,math)
values(7,'何北',75,81,80);

insert into
student(id,name,chinese,english,math)
values(8,'唐娇',77,80,79);

insert into
student(id,name,chinese,english,math)
values(9,'任知了',95,85,85);

insert into
student(id,name,chinese,english,math) values(10,'王越',94,85,84);

查询表中所有学生的信息。

select * from
student;

查询表中所有学生的姓名和对应的英语成绩。

select
name,english from student;

过滤表中重复数据。

select
english from student;

select
DISTINCT english from student;

select
DISTINCT english,name from student;

select
english+chinese+math from student;

select
english+chinese+math as 总分 from student;

select
name,english+chinese+math as 总分 from student;

在所有学生英语分数上加10分特长分。

select
name,english+10 from student;

统计每个学生的总分。

select
english+chinese+math from student;

使用别名表示学生分数

select
name,english+chinese+math as 总分 from student;

select
name,english+chinese+math 总分 from student;

查询姓名为何东的学生成绩

select * from
student where name='何东';

查询英语成绩大于90分的同学

select * from
student where english>90;

查询总分大于250分的所有同学

select * from
student where english+chinese+math>250;

查询英语分数在 85－95之间的同学。

select * from
student where english>=85 and english<=95;

select * from
student where english between 85 and 95;

查询数学分数为84,90,91的同学。

select * from
student where math=84 or math=90 or math=91;

select * from
student where math in(84,90,91);

查询所有姓何的学生成绩。

select * from
student where name like '何%';

查询数学分>85，语文分>90的同学。

select * from
student where math>85 and chinese>90;

对数学成绩排序后输出。

select * from
student order by math;

对总分排序后输出，然后再按从高到低的顺序输出

select * from
student order by math+chinese+english desc;

对姓何的学生成绩排序输出

select * from
student where name like '何%' order by math+chinese+english
desc;

select name,
math+chinese+english from student where name like '何%' order by
math+chinese+english desc;

统计一个班级共有多少学生？

select
count(*) from student;

统计数学成绩大于90的学生有多少个？

select
count(*) from student where math>90;

统计总分大于250的人数有多少？

select
count(*) from student where math+chinese+english>250;

统计一个班级数学总成绩？

select
sum(math) from student;

统计一个班级语文、英语、数学各科的总成绩

select
sum(math), sum(chinese), sum(english) from student;

统计一个班级语文、英语、数学的成绩总和

select
sum(math+chinese+english)from student;

select
sum(math)+sum(chinese)+sum(english) from student;

求一个班级数学平均分？

select
avg(math) from student;

求一个班级总分平均分

select
avg(math+chinese+english)from student;

select
avg(math)+avg(chinese)+avg(english) from student;

求班级最高分和最低分

select
max(math+chinese+english),min(math+chinese+english) from
student;

查出各个班的总分，最高分

准备环境

给表添加一个字段：alter
table student add column class_id int;

更新表：

update
student set class_id=1 where id<=5;

update
student set class_id=2 where id>5;

select
sum(math+chinese+english),max(math+chinese+english) from student
group by class_id;

查询出班级总分大于1300分的班级ID

select
class_id from student group by class_id having
sum(math+chinese+english)>1300;

表的约束　　

*定义主键约束　primary key:不允许为空，不允许重复

*定义主键自动增长　auto_increment

*定义唯一约束　unique

*定义非空约束　not null

*定义外键约束　constraint ordersid_FK foreign
key(ordersid) references orders(id)

*删除主键：alter table tablename drop primary key
;

数据的备份与恢复：

*准备数据：

create database mydb1;

use mydb1;

create table user(

id int,

name
varchar(20)

);

insert into user(id,name)
values(1,'Tom');

select * from user;

*备份：

mysqldump -uroot -p
mydb1>d:\test.sql;--备份数据库里的数据

*恢复；

mysql -uroot -p mydb1

source
d:\test.sql(在mysql客户端上执行)

多表查询与子查询：

准备环境：

部门表

CREATE TABLE
DEPARTMENT(

department_id int primary key
auto_increment,

name varchar

);

职位表

CREATE TABLE
LOCATION (

location_id int PRIMARY KEY
auto_increment,

name varchar

);

员工表

CREATE TABLE
EMPLOYEES(

employee_id int PRIMARY KEY
auto_increment,

department_id
int,

location_id
int,

first_name
varchar,

last_name
varchar,

salary double,

hire_date
date

);

向department表中添加数据

insert into
department(name) values ('人事');

insert into
department(name) values ('财务');

insert into
department(name) values ('后勤');

insert into
department(name) values ('公关');

insert into
department(name) values ('研发');

向location表中添加数据

insert into
location(name) values ('总经理');

insert into
location(name) values ('经理');

insert into
location(name) values ('主管');

insert into
location(name) values ('组长');

insert into
location(name) values ('职员');

向employees表中添加数据

insert into
employees(department_id,location_id , first_name, last_name,
salary,hire_date)

values (1,1, 'A', 'z', 50000,
'2005-02-21');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (1,2, 'B', 'x', 20000,
'2009-03-21');

insert into
employees(department_id,location_id , first_name, last_name,
salary,hire_date)

values (2,3, 'C', 'v', 10000,
'2009-08-23');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (4,2, 'D', 'n', 30000,
'2004-09-28');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (3,5, 'E', 'm', 3000,
'2009-04-11');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (5,5, 'F', 'l', 5000,
'2008-03-11');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (5,3, 'G', 'p', 20000,
'2005-05-09');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (5,4, 'H', 'o', 8000,
'2006-07-21');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (5,5, 'I', 'u', 6000,
'2006-09-21');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (5,5, 'J', 'y', 5500,
'2007-08-21');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (5,5, 'K', 't', 6500,
'2006-12-21');

insert into
employees(department_id,location_id, first_name, last_name,
salary,hire_date)

values (5,1, 'L', 'r', 100000, '2001-05-21');

练习：

--多表查询：查出姓z的员工的所有信息

select * from employees e,
department d, location l

where
e.[department_id]=d.[department_id] and
e.[location_id]=l.[location_id] and e.[last_name]='z';

--单行子查询: 查出所有工资大于平均工资的员工信息

select * from employees where
salary >(select avg(salary) from employees)

--多行子查询: 查出所有所有姓z的部门名称

select name from department
where department_id in (select department_id from employees where
last_name='z');