MariaDB数据库 ----数据库简介，用户管理，数据库创建，数据类型、数据增删改(实例演示)

数据库简介

数据库--即电子文件柜，用户可以对文件中的数据进行增，删，改，查等操作。

数据库分类

1. 关系型数据库
   
   关系型数据库管理系统（Relational Database Management System，RDBMS）
2. 非关系型数据库
   
   noSQL（Not Only SQL )

关系型数据库与非关系型数据库的区别

关系型数据库

1. 数据以二维表格的形式存储，可以通过外键关联，一致性强；
2. 数据存储在磁盘中，每次读取数据都是一次I/O请求，数度慢，系统开销大，高并发的情况下很影响性能
3. 使用方便，易于维护

非关系型数据库

1. 数据以key-value形式存储，只适合存储以一些简单的数据；不适合持久存储海量数据；
2. 数据存储在内存中，关联性弱，读取速度快；

常见关系型数据库管理系统

• Oracle
• Mysql
• MariaDB
• Microsoft SQL Server
• db2
• .......

常见非关系型数据库

• Redis
• MongoDB
• Amazon
• .......

MariaDB

MariaDB 数据库管理系统是Mysql的一个分支，是RDMS，主要由开源社区来维护；由于SUN被甲骨文公司收购，Mysql的所有权归oracle所有，不再开源。MySQL之父----Monty在2009年发起了MariaDB 开源项目。

MariaDB安装

MariaDB 10.3版本安装源

[mariadb]
name = MariaDB
baseurl = http://mirrors.ustc.edu.cn/mariadb/yum/10.3/centos7-amd64/
gpgkey=http://mirrors.ustc.edu.cn/mariadb/yum/RPM-GPG-KEY-MariaDB
gpgcheck=1

MariaDB数据类型

常用数据类型

• 整数型：int，bit
• 小数型：decimal #decimal(5,2)
• 字符串：varchar，char
• 时间：date，time，datetime
• 枚举类型：enum

约束

• primary key：主键
• not null：不为空
• unique：字段不重复
• default：默认
• foreign key：外键，对关系字段进行约束，当关系字段填写值时，会到关联的表中查询此值是否存在，如果存在则填写成功，如果不存在则填写失败并抛出异常。

数值类型常用

类型	字节大小	有符号范围（signed）	无符号范围（unsigned）
tinyint	1	-128~127	0~255
smallint	2	-32768~32767	0~65535
mediumint	3	-8388608~8388607	0~16777215
int/integer	4	-2147483648~2147483647	0~4294967295
bigint	8	-9223372036854775808~ 9223372036854775807	0~18446744073709551615

字符串

类型	字节大小	示例
char	0~255	不能伸缩（定多少我就取多少）
varchar	0~255	可以伸缩（要浪费一个字节指定字符长度）
text	0~65535	大文本

日期时间类型

类型	字节大小	示例
date	4	'2019-01-01'
time	3	'12:30:30'
datetime	8	'2019-01-01 12:30:30'
timestamp	4	'1970-01-01 00:00:01'UTC~'2038-01-01 00:00:01'UTC

SQL语句（命令）

数据库管理

• 忘记数据库的root密码怎么办？

vim /etc/my.conf.d/server.conf

[server]
skip-grant-tables   #添加

#重启数据库

#无密码登陆数据库

• 创建或修改密码初始化数据库

╭─root@localhost.localdomain ~
╰─➤  mysql_secure_installation   

• 进入RDBMS

╭─root@localhost.localdomain ~
╰─➤  mysql -uroot -p123456     #SQLuser和passward

• 退出RDBMS

MariaDB [mysql]> quit
Bye
╭─root@localhost.localdomain ~
╰─➤  

• 查看所有数据库

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
+--------------------+

• 创建数据库

MariaDB [(none)]> create database test1;
Query OK, 1 row affected (0.001 sec)

#指定字符编码
MariaDB [(none)]> create database test2 character set utf8;
Query OK, 1 row affected (0.003 sec)

• 设置与更改用户密码

SET PASSWORD FOR 'username'@'host' = PASSWORD('newpassword')

#如果是当前登陆用户
SET PASSWORD = PASSWORD("newpassword");

• 查看创建数据库的状态

MariaDB [test1]> show create database test1;
+----------+------------------------------------------------------------------+
| Database | Create Database                                                  |
+----------+------------------------------------------------------------------+
| test1    | CREATE DATABASE `test1` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+----------+------------------------------------------------------------------+

• 修改指定数据库的字符编码

MariaDB [test1]> alter database test1 default character set=utf8;
Query OK, 1 row affected (0.002 sec)

• 使用数据库

MariaDB [(none)]> use test1;
Database changed
MariaDB [test1]>     

• 删除数据库

MariaDB [test1]> drop database test2;
Query OK, 0 rows affected (0.005 sec)

用户管理

• 查看当前用户

MariaDB [test1]> select user();
+----------------+
| user()         |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.002 sec)

• 查看用户信息

用户信息储存在mysql数据库的user表

MariaDB [mysql]> select Host,User,Password from user;
+-----------+------+-------------------------------------------+
| Host      | User | Password                                  |
+-----------+------+-------------------------------------------+
| localhost | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
| 127.0.0.1 | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
| ::1       | root | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+-----------+------+-------------------------------------------+

• 在localhost主机上所有库所有表上给user250用户所有权限，认证密码'123456'

MariaDB [mysql]>-- grant 权限 on 库名.表 to 用户@主机 identified  by  '密码';

MariaDB [mysql]> grant all privileges on *.* to user250@localhost identified by '123456';
Query OK, 0 rows affected (0.003 sec)

• 给root用户在所有主机上的所有权限（用于第三方登录数据库）(端口号：3306)

MariaDB [(none)]> grant all privileges on *.* to root@'%' identified by '123456';
Query OK, 0 rows affected (0.001 sec)

MariaDB [(none)]> use mysql;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
MariaDB [mysql]> select host,user,password from user;
+-----------+---------+-------------------------------------------+
| host      | user    | password                                  |
+-----------+---------+-------------------------------------------+
| localhost | root    | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
| 127.0.0.1 | root    | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
| ::1       | root    | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
| %         | root    | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
| localhost | user250 | *6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9 |
+-----------+---------+-------------------------------------------+

• 给user250用户添加 查询 的权限

MariaDB [mysql]> grant select on *.* to user250@localhost ;
Query OK, 0 rows affected (0.000 sec)

select：查询权限

create：创建权限

update：更新权限

delete：删除权限

• 查看user250的权限

MariaDB [(none)]>-- show grants for 用户@主机；

MariaDB [(none)]> show grants for user250@localhost;

• 收回user250用户的所有权限

MariaDB [(none)]> revoke all on *.* from user250@localhost;
Query OK, 0 rows affected (0.001 sec)

表结构操作

• 显示当前时间

MariaDB [(none)]> select now();
+---------------------+
| now()               |
+---------------------+
| 2019-07-03 07:00:39 |
+---------------------+

• 创建葫芦娃表

MariaDB [test1]> create table huluwa (
    -> id int unsigned auto_increment primary key,
    -> name varchar(10),
    -> age tinyint unsigned,
    -> high decimal(5,2),
    -> gender enum('boy','girl','unknow')default 'unknow'
    -> );
Query OK, 0 rows affected (0.206 sec)

• 查看所有表

MariaDB [test1]> show tables;
+-----------------+
| Tables_in_test1 |
+-----------------+
| huluwa          |
+-----------------+

• 查看表结构

MariaDB [test1]> desc huluwa;
+--------+-----------------------------+------+-----+---------+----------------+
| Field  | Type                        | Null | Key | Default | Extra          |
+--------+-----------------------------+------+-----+---------+----------------+
| id     | int(10) unsigned            | NO   | PRI | NULL    | auto_increment |
| name   | varchar(10)                 | YES  |     | NULL    |                |
| age    | tinyint(3) unsigned         | YES  |     | NULL    |                |
| high   | decimal(5,2)                | YES  |     | NULL    |                |
| gender | enum('boy','girl','unknow') | YES  |     | unknow  |                |
+--------+-----------------------------+------+-----+---------+----------------+

• 给表添加字段

MariaDB [test1]>-- alter table 表名 add 列名 类型;

MariaDB [test1]> alter table huluwa add color varchar(10);
Query OK, 0 rows affected (0.406 sec)
Records: 0  Duplicates: 0  Warnings: 0

• 修改表字段；不重命名（modify）

MariaDB [test1]>-- alter table 表名 modify 列名 类型及约束；

MariaDB [test1]> alter table huluwa modify name varchar(20);
Query OK, 0 rows affected (0.005 sec)
Records: 0  Duplicates: 0  Warnings: 0

• 修改表字段；重命名

MariaDB [test1]>-- alter table 表名 change 原名 新名 类型及约束;

MariaDB [test1]> alter table huluwa change age bir_day date;
Query OK, 0 rows affected (0.426 sec)
Records: 0  Duplicates: 0  Warnings: 0

• 删除字段

MariaDB [test1]>-- alter table 表名 drop 列名；

MariaDB [test1]> alter table huluwa drop color;
Query OK, 0 rows affected (0.018 sec)
Records: 0  Duplicates: 0  Warnings: 0

• 删除表

MariaDB [test1]>-- drop table 表名;

MariaDB [test1]> drop table huluwa;
Query OK, 0 rows affected (0.010 sec)

表数据 增，删，改

注意：bit 型数据有值只是终端显示不明显

• 创建表

MariaDB [test]> create table huluwa (
    ->  id int unsigned auto_increment primary key,
    ->  name varchar(10),
    ->  age tinyint unsigned,
    ->  high decimal(5,2),
    ->  gender enum('boy','girl','unknow')default 'unknow',
    ->  lost bit(1));

• 表结构

MariaDB [test1]> desc huluwa;
+--------+-----------------------------+------+-----+---------+----------------+
| Field  | Type                        | Null | Key | Default | Extra          |
+--------+-----------------------------+------+-----+---------+----------------+
| id     | int(10) unsigned            | NO   | PRI | NULL    | auto_increment |
| name   | varchar(10)                 | YES  |     | NULL    |                |
| age    | tinyint(3) unsigned         | YES  |     | NULL    |                |
| high   | decimal(5,2)                | YES  |     | NULL    |                |
| gender | enum('boy','girl','unknow') | YES  |     | unknow  |                |
| lost   | bit(1)                      | YES  |     | NULL    |                |
+--------+-----------------------------+------+-----+---------+----------------+

• 查询表创建状态

MariaDB [test1]> show create table huluwa;

• 增加：全列插入(大娃出生了)

MariaDB [test1]>-- insert into 表名 values (...);

MariaDB [test1]> insert into huluwa values (0,'大娃',1,1.324,'boy',0);
Query OK, 1 row affected, 1 warning (0.003 sec)

MariaDB [test1]> select * from huluwa;
+----+--------+------+------+--------+------+
| id | name   | age  | high | gender | lost |
+----+--------+------+------+--------+------+
|  1 | 大娃   |    1 | 1.32 | boy    |      |
+----+--------+------+------+--------+------+

• 修改：（大娃丢了，lost列变为1）

MariaDB [test1]>-- update 表名 set 列=值... where 过滤条件；

MariaDB [test1]> update huluwa set lost=1 where name='大娃';
Query OK, 1 row affected (0.003 sec)
Rows matched: 1  Changed: 1  Warnings: 0

MariaDB [test1]> select * from huluwa;
+----+--------+------+------+--------+------+
| id | name   | age  | high | gender | lost |
+----+--------+------+------+--------+------+
|  1 | 大娃   |    1 | 1.32 | boy    |     |
+----+--------+------+------+--------+------+

• 数字类型数据可以使用运算符
• in（' ',' ',' '）语法的使用

update huluwa set age=age+1 where name in('大娃','二娃');

• 增加：部分插入（二娃出生了）

MariaDB [test1]>-- insert into 表名（字段） valuse（...）;

MariaDB [test1]> insert into huluwa(id, name,lost) values(0,'二娃',0);
Query OK, 1 row affected (0.003 sec)

MariaDB [test1]> select * from huluwa;
+----+--------+------+------+--------+------+
| id | name   | age  | high | gender | lost |
+----+--------+------+------+--------+------+
|  1 | 大娃   |    1 | 1.32 | boy    |     |
|  2 | 二娃   | NULL | NULL | unknow |      |
+----+--------+------+------+--------+------+

• 增加：插入多条（三娃和四娃一起出生了）

MariaDB [test1]>-- insert into 表名 valuse (...),(...),...;

MariaDB [test1]> insert into huluwa(id, name,lost) values(0,'三娃',0),(0,'四娃',0);
Query OK, 2 rows affected (0.003 sec)
Records: 2  Duplicates: 0  Warnings: 0

MariaDB [test1]> select * from huluwa;
+----+--------+------+------+--------+------+
| id | name   | age  | high | gender | lost |
+----+--------+------+------+--------+------+
|  1 | 大娃   |    1 | 1.32 | boy    |     |
|  2 | 二娃   | NULL | NULL | unknow |      |
|  3 | 三娃   | NULL | NULL | unknow |      |
|  4 | 四娃   | NULL | NULL | unknow |      |
+----+--------+------+------+--------+------+

• 删除（delete / truncate）（删除丢了的葫芦娃）

MariaDB [test1]>-- delete from 表名 where 条件;

MariaDB [test1]> delete from huluwa where lost=1;

MariaDB [test1]> select * from huluwa;
+----+--------+------+------+--------+------+
| id | name   | age  | high | gender | lost |
+----+--------+------+------+--------+------+
|  2 | 二娃   | NULL | NULL | unknow |      |
|  3 | 三娃   | NULL | NULL | unknow |      |
|  4 | 四娃   | NULL | NULL | unknow |      |
+----+--------+------+------+--------+------+

MariaDB [test1]> truncate table huluwa;
Query OK, 0 rows affected (0.040 sec)

MariaDB [test1]> show tables;
+-----------------+
| Tables_in_test1 |
+-----------------+
| huluwa          |
+-----------------+
1 row in set (0.000 sec)

MariaDB [test1]> select * from huluwa;
Empty set (0.000 sec)

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