关系型数据库介绍
数据结构模型
数据结构模型主要有：
- 层次模型
- 网状结构
- 关系模型
关系模型：
二维关系：row，column
数据库管理系统：DBMS
关系：Relational，RDBMS
RDBMS专业名词
常见的关系型数据库管理系统：
- MySQL：MySQL，MariaDB，Percona-Server
- PostgreSQL：简称为pgsql
- Oracle
- MSSQL
事务：多个操作被当作一个整体对待就称为一个事务
要看一个关系型数据库是否支持事务，需要看其是否支持并满足ACID测试
ACID：ACID是事务的一个基本标准
- A：Automicity，原子性
- C：Consistency，一致性
- I：Isolation，隔离性
- D：Durability，持久性
如果你对ACID感兴趣，可以查看这里了解详细说明，ACID将不作为我们讲解的重点。
SQL：Structure Query Language，结构化查询语言
约束：constraint，向数据表提供的数据要遵守的限制
- 主键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。且必须提供数据，不能为空（NOT NULL）。
一个表只能存在一个 - 惟一键约束：一个或多个字段的组合，填入的数据必须能在本表中唯一标识本行。允许为空（NULL）
一个表可以存在多个 - 外键约束：一个表中的某字段可填入数据取决于另一个表的主键已有的数据
检查性约束
索引：将表中的一个或多个字段中的数据复制一份另存，并且这些数据需要按特定次序排序存储
关系运算：
- 选择：挑选出符合条件的行（部分行）
- 投影：挑选出需要的字段
- 连接
数据抽象方式：
- 物理层：决定数据的存储格式，即RDBMS在磁盘上如何组织文件
- 逻辑层：描述DB存储什么数据，以及数据间存在什么样的关系
- 视图层：描述DB中的部分数据
关系型数据库的常见组件
关系型数据库的常见组件有：
- 数据库：database
- 表：table，由行（row）和列（column）组成
- 索引：index
- 视图：view
- 用户：user
- 权限：privilege
- 存储过程：procedure
- 存储函数：function
- 触发器：trigger
- 事件调度器：event scheduler
SQL语句
SQL语句有三种类型：
- DDL：Data Defination Language，数据定义语言
- CREATE：创建
- DROP：删除
- ALTER：修改
- DML：Data Manipulation Language，数据操纵语言
- INSERT：向表中插入数据
- DELETE：删除表中数据
- UPDATE：更新表中数据
- SELECT：查询表中数据
- DCL：Data Control Language，数据控制语言
- GRANT：授权
- REVOKE：移除授权
mysql安装与配置
安装mysql
#配置yum源
[root@YingMo ~]# cd /usr/src/
[root@YingMo src]# ls
debug kernels
[root@YingMo src]# wget http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm
[root@YingMo src]# yum -y install mysql57-community-release-el7-10.noarch.rpm
[root@YingMo src]# ls /etc/yum.repos.d/
CentOS-Base.repo epel.repo mysql-community.repo mysql-community-source.repo
#可以看到已经有了mysql源了
#接下来安装mysql，安装mysql涉及四个包，分别为mysql-community-server、mysql-community-client、mysql-community-common和mysql-community-devel
[root@YingMo src]yum -y install mysql-community-server mysql-community-client mysql-community-common mysql-community-devel
配置mysql
#先启动mysql
[root@YingMo ~]# systemctl start mysqld
[root@YingMo ~]# systemctl status mysqld
● mysqld.service - MySQL Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
Active: active (running) since Fri 2019-02-15 15:00:12 CST; 8s ago
Docs: man:mysqld(8)
http://dev.mysql.com/doc/refman/en/using-systemd.html
Process: 26071 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid $MYSQLD_OPTS (code=exited, status=0/SUCCESS)
Process: 25997 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
Main PID: 26075 (mysqld)
CGroup: /system.slice/mysqld.service
└─26075 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid
Feb 15 15:00:08 YingMo systemd[1]: Starting MySQL Server...
Feb 15 15:00:12 YingMo systemd[1]: Started MySQL Server.
#确保3306端口处于监听状态
[root@YingMo ~]# ss -antl
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN 0 128 *:22 *:*
LISTEN 0 80 :::3306 :::*
#找到临时密码
[root@YingMo ~]# grep "password" /var/log/mysqld.log
2019-02-15T07:00:09.467221Z 1 [Note] A temporary password is generated for root@localhost: g(=mj,K_r1gg
#使用临时密码登陆mysql
[root@YingMo ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 2
Server version: 5.7.25
Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.
mysql>
#看到上面“mysql>”代表登录成功
#修改mysql登陆密码
#将密码安全性检查调到LOW
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)
#将密码最大长度设置为1（因为是测试环境，所以改成了1，生产环境最好还是长一些）
mysql> set global validate_password_length=1;
Query OK, 0 rows affected (0.00 sec)
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'lynk';
Query OK, 0 rows affected (0.00 sec)
#如果不想改变validate_password_policy参数，保持默认，那么密码必须包含有数字、小写或大写字母、特殊字符
mysql> quit
Bye
#为了防止更新我们要卸掉最开始安装的yum源。因为更新后可能会存在不稳定的情况，这种问题还是能避免就避免一下的比较好。
[root@YingMo ~]# rpm -qa|grep mysql
mysql-community-common-5.7.25-1.el7.x86_64
mysql-community-libs-5.7.25-1.el7.x86_64
mysql-community-server-5.7.25-1.el7.x86_64
mysql57-community-release-el7-10.noarch
mysql-community-libs-compat-5.7.25-1.el7.x86_64
mysql-community-client-5.7.25-1.el7.x86_64
mysql-community-devel-5.7.25-1.el7.x86_64
[root@YingMo ~]# yum -y remove mysql57-community-release-el7-10.noarch
mysql工具的使用
#语法:mysql [OPTIONS] [database]
#常用OPTIONS：
-uUSERNAME 指定用户名，默认root
-hHOST 指定服务器主机，默认为localhost,推荐使用ip地址
-pPASSWORD 指定用户的密码
-P# 指定数据库监听的端口，这里的#需用实际的端口号代替，如-P3307
-V 查看当前使用的mysql版本
-e 不登录mysql执行sql语句后退出，常用于脚本
[root@YingMo ~]# mysql -uroot -p -h127.0.0.1
#注意:不建议在命令行中直接使用密码登陆，因为日志系统会将用户命令记录下来，导致密码泄露。建议使用-p选项，用交互式命令输入密码。
服务器监听的两种socket地址
- ip socket：默认监听在tcp的3306端口，支持远程通讯
- unix socket：监听在sock文件上（/tmp/mysql.sock，/var/lib/mysql/mysql.sock）仅支持本地通讯
- server地址只能是：localhost，127.0.0.1
应用实例
创建一个以lynk为名的数据库，创建一张表student，该表包含三个字段（id，name，age），表结构如下
mysql> desc student;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | int(11) | NO | | NULL | |
| name | varchar(100) | NO | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.00 sec)
mysql> use lynk;
Database changed
mysql> CREATE TABLE student (id int(11),name varchar(100),age tinyint(4) NULL);
Query OK, 0 rows affected (0.20 sec)
mysql> desc student;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| name | varchar(100) | YES | | NULL | |
| age | tinyint(4) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
3 rows in set (0.15 sec)
查看下该新建的表有无内容（用select语句）
mysql> select * from student;
Empty set (0.00 sec)
往新建的student表中插入数据（用insert语句）
mysql> insert student VALUES (1,'tom',20),(2,'jerry',23),(3,'wangqing',25),(4,'sean',28),(5,'zhangshan',26),(6,'zhangshan',20),(7,'lisi',NULL),(8,'chenshuo',10),(9,'wangwu',3),(10,'qiuyi',15),(11,'qiuxiaotian',20);
Query OK, 11 rows affected (0.04 sec)
Records: 11 Duplicates: 0 Warnings: 0
mysql> select * from student;
+------+-------------+------+
| id | name | age |
+------+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 6 | zhangshan | 20 |
| 7 | lisi | NULL |
| 8 | chenshuo | 10 |
| 9 | wangwu | 3 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+------+-------------+------+
11 rows in set (0.00 sec)
修改lisi的年龄为50
mysql> update student set age = 50 where name = 'lisi';
Query OK, 1 row affected (0.80 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from student;
+------+-------------+------+
| id | name | age |
+------+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 6 | zhangshan | 20 |
| 7 | lisi | 50 |
| 8 | chenshuo | 10 |
| 9 | wangwu | 3 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+------+-------------+------+
11 rows in set (0.00 sec)
以age字段降序排序
mysql> select * from student order by age desc;
+------+-------------+------+
| id | name | age |
+------+-------------+------+
| 7 | lisi | 50 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 3 | wangqing | 25 |
| 2 | jerry | 23 |
| 1 | tom | 20 |
| 6 | zhangshan | 20 |
| 11 | qiuxiaotian | 20 |
| 10 | qiuyi | 15 |
| 8 | chenshuo | 10 |
| 9 | wangwu | 3 |
+------+-------------+------+
11 rows in set (0.03 sec)
查询student表中年龄最小的3位同学
mysql> select * from student order by age limit 3;
+------+----------+------+
| id | name | age |
+------+----------+------+
| 9 | wangwu | 3 |
| 8 | chenshuo | 10 |
| 10 | qiuyi | 15 |
+------+----------+------+
3 rows in set (0.00 sec)
查询student表中年龄最大的4位同学
mysql> select * from student order by age desc limit 4;
+------+-----------+------+
| id | name | age |
+------+-----------+------+
| 7 | lisi | 50 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 3 | wangqing | 25 |
+------+-----------+------+
4 rows in set (0.00 sec)
查询student表中名字叫zhangshan的记录
mysql> select * from student where name = 'zhangshan';
+------+-----------+------+
| id | name | age |
+------+-----------+------+
| 5 | zhangshan | 26 |
| 6 | zhangshan | 20 |
+------+-----------+------+
2 rows in set (0.01 sec)
查询student表中名字叫zhangshan且年龄大于20岁的记录
mysql> select * from student where name = 'zhangshan' and age > 20;
+------+-----------+------+
| id | name | age |
+------+-----------+------+
| 5 | zhangshan | 26 |
+------+-----------+------+
1 row in set (0.02 sec)
查询student表中年龄在23到30之间的记录
mysql> select * from student where age between 23 and 30;
+------+-----------+------+
| id | name | age |
+------+-----------+------+
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
+------+-----------+------+
4 rows in set (0.00 sec)
修改wangwu的年龄为100
mysql> update student set age = 100 where name = 'wangwu';
Query OK, 1 row affected (1.35 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from student;
+------+-------------+------+
| id | name | age |
+------+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 6 | zhangshan | 20 |
| 7 | lisi | 50 |
| 8 | chenshuo | 10 |
| 9 | wangwu | 100 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+------+-------------+------+
11 rows in set (0.00 sec)
删除student中名字叫zhangshan且年龄小于等于20的记录
mysql> delete from student where name = 'zhangshan' and age <= 20;
Query OK, 1 row affected (0.06 sec)
mysql> select * from student;
+------+-------------+------+
| id | name | age |
+------+-------------+------+
| 1 | tom | 20 |
| 2 | jerry | 23 |
| 3 | wangqing | 25 |
| 4 | sean | 28 |
| 5 | zhangshan | 26 |
| 7 | lisi | 50 |
| 8 | chenshuo | 10 |
| 9 | wangwu | 100 |
| 10 | qiuyi | 15 |
| 11 | qiuxiaotian | 20 |
+------+-------------+------+
10 rows in set (0.00 sec)