5分钟带你快速回顾MySQL基础语法

快速回顾MySQL基础语法

1.安装

略 参考资料

2.数据库操作

• 查看所有数据库

  show databases;
  # mysql 用分号结束语句
  

• 创建数据库

  # create database [name]
  create database test
  

• 删除数据库

  drop database test
  

• 使用数据库

  # use [name]
  use test;
  

3.表操作

• 创建表

  create table test(
      id int,
      name varchar(10),
      age int,
      gender char(2),
      birthday date,
      tel char(11),
      email varchar(30)
  );
  

• 删除表

  # drop table [name]
  drop table test;
  

• 字段约束

  1. 主键 primary key:用来唯一标识一条记录的字段
  2. 非空 not null：所修饰字段值不能为空
  3. 外键 foreign key：外键标识当前字段的取值只能来自于外键所指定的字段中的值，或者为null
  4. 自增长 auto_increment：插入数据时自动增长的字段

  # create table department
  create table department(
      id int primary key auto_increment,
      name varchar(30) not null,
      tel char(11)
  );
  

  CREATE TABLE class (
  id int NOT NULL AUTO_INCREMENT,
  name varchar(10) DEFAULT NULL,
  depId int DEFAULT NULL,
  PRIMARY KEY (id),
  FOREIGN KEY (id) REFERENCES department(id) ON DELETE CASCADE ON UPDATE RESTRICT
  );
  

• 查看当前数据库的所有表

  show tables;
  

• 查看表结构

  # desc [table_name]
  desc class;
  

• 修改表 alter table

  修改内容	关键词	语法
  添加列	add	alter table [表名] add [列名] [类型] [约束]
  修改列	modify	alter table [表名] modofy [列名] [类型] [约束]
  列重命名	change	alter table [表名] change [旧列名] [ 新列名] [类型] [约束]
  删除列	drop	alter table [表名] drop [列名]
  表重命名	rename	rename table [旧表名] to [新表名]
  修改表的字符集	character set	alter table [表名] character set [字符集名称]

  rename table test to student;
  
  alter table student add grade int;
  
  alter table student modify id  int primary key auto_increment;
  
  alter table student change birthday  birth date;
  
  alter table student drop age;
  

4.数据插入

insert into department(id,name,tel) value(1,'dep1','123456');

insert into department(name,tel) value('dep2','123456');

insert into department(name) value('dep2');# 这条记录id为3

insert into department value(4,'dep3','123456');

5.数据删除

delete from department where id =3;

6.数据更新

update department set name='dep5' where id=4;

# 使用某一列的值给其他列赋值
update department set name=tel;

7.数据查询

#===============单表查询=================

# 查询student表中所有字段；
select * from student;

# 查询student表中特定字段；
select id name from student;
select name, grade from student;

# 查询结果起别名
select name 姓名 ,grade 成绩  from student;

#查询不重复的姓名
select distinct name from student

# 查询成绩>60的学生学号，姓名和成绩
select id,name,grade from student where grade>60;

# 查询总人数
select count(*) 总人数 from student;

# 查询总人数，总成绩，平均分
select count(*) 总人数,sum(grade) 总成绩,sum(grade)/count(*) 平均分  from student;


#查询结果排序
select * from student order by grade;
select * from student order by grade desc;#降序排列

# 分组查询
##查询男女生人数
select gender,count(*) from student group by gender;
## 查询各个分数有多少人
select grade,count(*) from student group by grade;


#===============多表查询=================

# 查询班级，系名，电话
select class.name, department.name, tel from class ,department  where class.depId=department.id;
select c.name, d.name, tel from class c ,department d  where c.depId=d.id;# 使用别名

# 左连接
select c.name, d.name, tel from class c left join department d on c.depId=d.id ;

# 右连接
select c.name, d.name, tel from class c right join department d on c.depId=d.id ;

8.用户管理

用户信息在mysql默认数据库mysql.user中保存

#查看用户
select user ,host from user;

+------------------+-----------+
| user             | host      |
+------------------+-----------+
| mysql.infoschema | localhost |
| mysql.session    | localhost |
| mysql.sys        | localhost |
| root             | localhost |
+------------------+-----------+

# user :用户名
# host:主机地址

#添加用户
create user 'lisi'@'localhost' identified by '123456';
#删除用户
drop user 'lisi@localhost';

9.权限管理

用户权限信息在mysql默认数据库mysql.user中保存

#查看用户权限
 show grants for 'root'@'localhost';
 
# 授予用户权限
#grant 权限列表 on 数据库.表名 to 'user'@'host'
• grant select,update,delete on test.* to 'lisi'@'localhost'
grant all on *.* to 'lisi'@'localhost'
 
# 撤销权限授予
# revoke 权限列表 on  数据库名.表名 from 'username'@'host'