一、MySQL数据库简介
数据库服务概述
常见的数据库软件
主流操作系统 Unix、Linux、Windows
专业术语
DB (DataBase)
-数据库
-依照某种数据模型进行组织并存放到存储器的数据集合
DBMS(DataBase Mangement System)
- 数据库管理系统
- 用来操纵和管理数据库的服务软件
DBS(DataBase System)
-数据库系统:即 DB+ DBMS
-指带有数据库并整合了数据库管理软件的计算机系统
起源与发展
-应用最广泛的开源数据库软件
-一最早隶属于瑞典的MySQL AB公司
-2008年1月，MySQL AB被Sun收购
-2009年4月，SUN被Oracle收购
崭新的开源分支MariaDB
-为应付MySQL可能会闭源的风险而诞生
-由MySQL原作者 Widenius主导开发-与MySQL保持最大程度兼容
-MariaDB的目的是完全兼容MySQL，包括API和命令行，使之能轻松成为MySQL的代替品。
特点及应用
主要特点
-适用于中小规模、关系型数据库系统
-支持Linux、Unix、Windows等多种操作系统
-支持Python、Java、Perl、PHP等编程语言
典型应用环境
-LAMP平台，与Apache HTTP Server组合
-LNMP平台，与Nginx组合
二、MySQL数据的安装
2.1、MySQL安装
准备环境 基本需求
1．创建CentOS系统虚拟机1台
2．配置IP地址192.168.4.150
3．关闭firewalld
4．禁用SELinux
5．配置yum源 安装mysql-server
1 ) 安装MySQL 配置官网的yum源
[root@mysql ~]# rpm -ivh mysql80-community-release-el7-3.noarch.rpm #安装官方yum源
[root@mysql ~]# yum clean all
[root@mysql ~]# yum repolist
[root@mysql ~]# yum -y install mysql-server #安装MySQL服务端
[root@mysql ~]# rpm -qa |grep mysql
mysql-community-client-8.0.22-1.el7.x86_64 #客户端应用程序
mysql80-community-release-el7-3.noarch #之前下载的 yum安装包
mysql-community-common-8.0.22-1.el7.x86_64 #数据库和客户端库共享文件
mysql-community-libs-8.0.22-1.el7.x86_64 #数据库客户端应用程序的共享库
mysql-community-client-plugins-8.0.22-1.el7.x86_64
mysql-community-server-8.0.22-1.el7.x86_64 #数据库服务端
[root@mysql ~]# systemctl start mysqld #开启服务
[root@mysql ~]# systemctl enable mysqld #设置开机启动
[root@mysql ~]# systemctl status mysqld #查看服务状态
● mysqld.service - MySQL Server
Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
Active: active (running) since 二 2020-11-24 14:07:31 CST; 4min 21s ago
Docs: man:mysqld(8)
http://dev.mysql.com/doc/refman/en/using-systemd.html
Process: 2919 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
Main PID: 2991 (mysqld)
Status: "Server is operational"
CGroup: /system.slice/mysqld.service
└─2991 /usr/sbin/mysqld
11月 24 14:07:09 mysql systemd[1]: Starting MySQL Server...
11月 24 14:07:31 mysql systemd[1]: Started MySQL Server.
[root@mysql ~]# ss -anput|grep 3306 #查看服务占用端口
tcp LISTEN 0 70 :::33060 :::* users:(("mysqld",pid=2991,fd=32))
tcp LISTEN 0 128 :::3306 :::* users:(("mysqld",pid=2991,fd=34))软件安装后自动创建相关目录文件
主配置文件
-/etc/my.cnf
数据库目录
-/var/lib/mysql
默认端口号: 3306
进程名 mysqld
传输协议 TCP
进程所有者 mysql
进程所属组 mysql
错误日志文件
-/var/log/mysqld.log
2 ) 初始密码登录
数据库管理员名为root
- 默认仅允许root本机连接
- 首次登录密码在安装软件时随机生成
- 随机密码存储在日志文件/var/log/mysqld.log里
- 连接命令 ]# mysql -h数据库地址 -u用户 -p密码
- 数据库命令输入默认不支持 Tab键命令补齐,这也进一步增加了数据管理员的难度,在日常的使用管理中,管理员一般会借助第三方的数据库管理软件
常用的数据库管理软件有:
-Workbench
-Navicat
2.2、修改MySQL密码登录策略
案例1:
要求:登陆数据库修改密码策略 设置简单密码
[root@mysql ~]# grep -i 'password' /var/log/mysqld.log //查看随机密码
2020-11-24T06:07:17.500550Z 6 [Note] [MY-010454] [Server] A temporary password is generated for root@localhost: R-SsjKcfZ4a7
[root@mysql ~]# mysql -u root -p'R-SsjKcfZ4a7' //登陆mysql
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 20
Server version: 8.0.22
Copyright (c) 2000, 2020, 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> //登录成功后，进入SQL操作环境
mysql> show databases;
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement. #提示需要修改默认密码修改root密码
-具体操作如下
-使用alter user命令修改登录密码―新密码必须满足密码策略
修改登陆密码方法如下:
mysql> alter user root@"localhost " identified by“密码";连接MySQL服务器时，最基本的用法是通过 -u 选项指定用户名、-p指定密码。密码
可以写在命令行（如果不写，则出现交互，要求用户输入），当然基于安全考虑一般
不推荐这么做：所以以下明文密码会有警告!
[Warning] Using a password on the command line interface can be insecure.
mysql> alter user root@"localhost" identified by "123AAA...b"; //修改密码
Query OK, 0 rows affected (0.03 sec)
mysql> exit //退出数据库 或使用 quit
Bye
[root@mysql ~]# mysql -u root -p'123AAA...b'
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 23
Server version: 8.0.22 MySQL Community Server - GPL
Copyright (c) 2000, 2020, 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> 3 ) 修改密码策略
为了方便后面的演示,输入密码不用太复杂设置一个简单的密码 默认数据库是有密码复杂度要求的
临时生效 服务重启后失效
mysql> set global validate_password.policy=0; //只验证长度
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password.length=6; //修改密码长度为6位,默认为8位
Query OK, 0 rows affected (0.00 sec)
mysql> alter user root@"localhost" identified by "123456"; //修改密码为123456
Query OK, 0 rows affected (0.04 sec)
mysql> exit
Bye修改配置文伯 永久性生效
[root@mysql ~]# vim /etc/my.cnf
[mysqld] //在mysqld后面添加这两行
validate_password.policy=0
validate_password.length=6
[root@mysql ~]# systemctl restart mysqld
[root@mysql ~]# mysql -u root -p123456 //登陆MySQL
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 24
Server version: 8.0.22 MySQL Community Server - GPL
Copyright (c) 2000, 2020, 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> show databases; //显示已有的库
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
4 rows in set (0.06 sec)
mysql> 三、数据库基础管理
3.1、连接方式及数据储存流程
客户端连接MySQL服务的方法
1.命令行
2.web页面
3.安装图形软件
4.编写脚本（ php、Java、python.....)
-使用 mysql 命令登录
mysql -h服务器IP -u用户名 -p密码「数据库名]
-quit或exit退出
数据存储流程
客户端把数据存储到数据库服务器上的步骤
1.连接数据库服务器
2.建库 //类似于文件夹
3.建表 //类似于文件
4.插入记录 //类似于文件内容
5.断开连接
SQL命令使用规则
- SQL命令不区分字母大小写（密码、变量值除外)
- 每条SQL命令以 ; 结束
- 默认命令不支持Tab键自动补齐
- \c 终止sql命令
MySQL管理环境（续1)
常用的SQL命令分类
管理数据库使用SQL（结构化查询语言)
1.DDL数据定义语言 如:create、alter、drop
2.DML数据操作语言 如:insert、update、delete
3.DCL数据控制语言 如:grant、revoke
4.DTL数据事物语言 如:commit、rollback、savepoint
3.2、库管理命令
库管理命令
- 库类似于文件夹，用来存储表
- 可以创建多个库，通过库名区分
- show databases; #显示已有的库
- select user( ); #显示连接用户
- use 库名; #切换库
- select database( ); #显示当前所在的库
- create database 库名; #创建新库
- show tables; #显示已有的表
- drop database 库名; #删除库
库管理命令（续1)
库名命名规则
- 仅可以使用数字、字母、下划线、不能纯数字
- 区分字母大小写，具有唯一性
不可使用指令关键字、特殊字符
mysql> create database DB1; Query OK, 1 row affected (0.03 sec) mysql> CREATE DATABASE db1; Query OK, 1 row affected (0.04 sec)3.3、表管理命令
·建表
-表存储数据的文件。
Mysql> create table 库名.表名(字段名1 类型(宽度), 字段名2 类型(宽度), ......)DEFAULT CHARSET=utf8; #指定中文字符集，可以给字段赋值中文
mysql> create table db1.stuinfo(
name char(15),
homeaddr char(20)
表管理命令（续1)
- 表类似于文件,
- desc库名.表名; #查看表结构
- drop table库名.表名; #删除表
3.4、记录管理命令
- 记录类似于文件里的行
- select * from库名.表名; #查看表记录
- insert into库名.表名 values(值列表); #插入表记录
- update 库名.表名 set字段=值; #修改表记录
delete from表名; #删除表记录
mysq> insert into db1.stuinfo values("jim" ;" usa"),("lilei" , "china"); mysql> select * from db1.stuinfo; Mysql> update db1.stuinfo set homeaddr= "beijing" ;案例2∶数据库基本管理
1.使用mysql命令连接数据库 新建如下表格
2.练习库管理命令(查看、删除、创建库、切换）
3.练习表管理命令(查看、删除、创建表)
4.练习记录管理命令(插入、查看、修改、删除)
1 ) 使用mysql命令连接数据库,练习查看现在的库
[root@mysql ~]# mysql -u root -p123456
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| DB1 |
| db1 |
| information_schema | //信息概要库
| mysql | //授权库
| performance_schema | //性能结构库
| sys | //系统元数据库
+--------------------+
6 rows in set (0.06 sec)2）切换/使用指定的库
mysql> use sys; //切换到sys库
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
mysql> select database(); //确认当前所在的库
+------------+
| database() |
+------------+
| sys |
+------------+
1 row in set (0.00 sec)
mysql> use mysql; //切换到mysql库
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
mysql> select database(); //确认当前所在的库
+------------+
| database() |
+------------+
| mysql |
+------------+
1 row in set (0.00 sec)3）新建名为newdb的库，确认结果
mysql> create database newdb; //新建名为newdb的库
Query OK, 1 row affected (0.03 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| DB1 |
| db1 |
| information_schema |
| mysql |
| newdb | //新建的newdb库
| performance_schema |
| sys |
+--------------------+
7 rows in set (0.01 sec)4）删除指定的库
mysql> drop database newdb; //删除名为newdb的库
Query OK, 0 rows affected (0.02 sec)
mysql> show databases; //确认删除结果，已无newdb库
+--------------------+
| Database |
+--------------------+
| DB1 |
| db1 |
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
6 rows in set (0.00 sec)5）查看指定的库里有哪些表
mysql> use mysql
Database changed
mysql> use mysql;
Database changed
mysql> show tables;
+----------------------------------------------+
| Tables_in_mysql |
+----------------------------------------------+
| columns_priv |
| component |
| db |
| default_roles |
| engine_cost |
| func |
| general_log |
| global_grants |
| gtid_executed |
| help_category |
| help_keyword |
| help_relation |
| help_topic |
| innodb_index_stats |
| innodb_table_stats |
| password_history |
| plugin |
| procs_priv |
| proxies_priv |
| replication_asynchronous_connection_failover |
| role_edges |
| server_cost |
| servers |
| slave_master_info |
| slave_relay_log_info |
| slave_worker_info |
| slow_log |
| tables_priv |
| time_zone |
| time_zone_leap_second |
| time_zone_name |
| time_zone_transition |
| time_zone_transition_type |
| user | //存放数据库用户的表
+----------------------------------------------+
34 rows in set (0.00 sec)6）查看指定表的字段结构
当前库为mysql，查看columns_priv表的结构，以列表形式展现
mysql> desc columns_priv\G
*************************** 1. row ***************************
Field: Host
Type: char(255)
Null: NO
Key: PRI
Default:
Extra:
*************************** 2. row ***************************
Field: Db
Type: char(64)
Null: NO
Key: PRI
Default:
Extra:
*************************** 3. row ***************************
Field: User
Type: char(32)
Null: NO
Key: PRI
Default:
Extra:
*************************** 4. row ***************************
Field: Table_name
Type: char(64)
Null: NO
Key: PRI
Default:
Extra:
*************************** 5. row ***************************
Field: Column_name
Type: char(64)
Null: NO
Key: PRI
Default:
Extra:
*************************** 6. row ***************************
Field: Timestamp
Type: timestamp
Null: NO
Key:
Default: CURRENT_TIMESTAMP
Extra: DEFAULT_GENERATED on update CURRENT_TIMESTAMP
*************************** 7. row ***************************
Field: Column_priv
Type: set('Select','Insert','Update','References')
Null: NO
Key:
Default:
Extra:
7 rows in set (0.00 sec)查看columns_priv表的结构，以表格形式展现
mysql> desc columns_priv; //查看表结构，以表格形式展现末尾需要有分号
+-------------+----------------------------------------------+------+-----+-------------------+-----------------------------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+----------------------------------------------+------+-----+-------------------+-----------------------------------------------+
| Host | char(255) | NO | PRI | | |
| Db | char(64) | NO | PRI | | |
| User | char(32) | NO | PRI | | |
| Table_name | char(64) | NO | PRI | | |
| Column_name | char(64) | NO | PRI | | |
| Timestamp | timestamp | NO | | CURRENT_TIMESTAMP | DEFAULT_GENERATED on update CURRENT_TIMESTAMP |
| Column_priv | set('Select','Insert','Update','References') | NO | | | |
+-------------+----------------------------------------------+------+-----+-------------------+-----------------------------------------------+
7 rows in set (0.00 sec)上述操作中，当引用非当前库中的表时，可以用“库名.表名”的形式。比如，切换
为mysql库再执行“desc columns_priv;”，与以下操作的效果是相同的：
mysql> desc mysql.columns_priv;
+-------------+----------------------------------------------+------+-----+-------------------+-----------------------------------------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+----------------------------------------------+------+-----+-------------------+-----------------------------------------------+
| Host | char(255) | NO | PRI | | |
| Db | char(64) | NO | PRI | | |
| User | char(32) | NO | PRI | | |
| Table_name | char(64) | NO | PRI | | |
| Column_name | char(64) | NO | PRI | | |
| Timestamp | timestamp | NO | | CURRENT_TIMESTAMP | DEFAULT_GENERATED on update CURRENT_TIMESTAMP |
| Column_priv | set('Select','Insert','Update','References') | NO | | | |
+-------------+----------------------------------------------+------+-----+-------------------+-----------------------------------------------+
7 rows in set (0.00 sec)在mydb库中创建一个名为pwlist的表
mysql> create database mydb;
Query OK, 1 row affected (0.28 sec)
mysql> use mydb
Database changed
mysql> create table pwlist(
-> name char(16) not null,
-> password char(48)default'',
-> primary key(name)
-> );
Query OK, 0 rows affected (0.39 sec)
mysql> show tables; //查看新建的表单
+----------------+
| Tables_in_mydb |
+----------------+
| pwlist |
+----------------+
1 row in set (0.01 sec)
mysql> desc pwlist; //查看pwlist表的字段结构
+----------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+-------+
| name | char(16) | NO | PRI | NULL | |
| password | char(48) | YES | | | |
+----------+----------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> drop table pwlist; //删除当前库中的pwlist表
Query OK, 0 rows affected (0.11 sec)案例3：
在mydb库中创建一个学员表
在MySQL表内存储中文数据时，需要更改字符集（默认为latin1不支持中文），以便
MySQL支持存储中文数据记录；比如，可以在创建库或表的时候，手动添加“DEFAULT
CHARSET=utf8”来更改字符集。
根据上述表格结构，创建支持中文的student表：
mysql> create table mydb.student(
-> 学号 char(9) NOT NULL,
-> 姓名 varchar(4) NOT NULL,
-> 性别 enum('男','女') NOT NULL,
-> 手机号 char(11) DEFAULT'',
-> 通信地址 varchar(64),
-> PRIMARY KEY(学号)
-> )DEFAULT CHARSET=utf8; //手工指定字符集，采用utf8
Query OK, 0 rows affected, 1 warning (0.04 sec)
mysql> DESC mydb.student; //查看student表的字段结构
+--------------+-------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-------------------+------+-----+---------+-------+
| 学号 | char(9) | NO | PRI | NULL | |
| 姓名 | varchar(4) | NO | | NULL | |
| 性别 | enum('男','女') | NO | | NULL | |
| 手机号 | char(11) | YES | | | |
| 通信地址 | varchar(64) | YES | | NULL | |
+--------------+-------------------+------+-----+---------+-------+
5 rows in set (0.00 sec)
mysql> show create table mydb.student; //查看student表的实际创建指令：
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | CREATE TABLE `student` (
`学号` char(9) NOT NULL,
`姓名` varchar(4) NOT NULL,
`性别` enum('男','女') NOT NULL,
`手机号` char(11) DEFAULT '',
`通信地址` varchar(64) DEFAULT NULL,
PRIMARY KEY (`学号`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+---------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
mysql> exit注意：若要修改MySQL服务的默认字符集，可以更改服务器的my.cnf配置文件，添加
character_set_server=utf8 配置，然后重启数据库服务。
[root@mysql ~]# cat /etc/my.cnf
[mysqld]
......
character_set_server=utf8 //添加默认字符集
[root@mysql ~]# systemctl restart mysqld //重启服务
[root@mysql ~]# mysql -u root -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.22 MySQL Community Server - GPL
Copyright (c) 2000, 2020, 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> show variables like 'character%';
+--------------------------+--------------------------------+
| Variable_name | Value |
+--------------------------+--------------------------------+
| character_set_client | utf8mb4 |
| character_set_connection | utf8mb4 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8mb4 |
| character_set_server | utf8 | //修改成功
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql-8.0/charsets/ |
+--------------------------+--------------------------------+
8 rows in set (0.01 sec)四、MySQL数据类型
4.1、常见信息种类
- 数值型∶体重、身高、成绩、工资
- 字符型:姓名、工作单位、通信住址
- 枚举型:兴趣爱好、性别、专业
- 日期时间型:出生日期、注册时间
4.2、字符型
定长char**
- 定长:char(字符个数)
- 最大字符个数255
- 不够指定字符个数时在右边用空格补全
- 字符个数超出时，无法写入数据。
mysql> create table db1.t1(
-> name char(5),
-> homedir char(50)
-> );
Query OK, 0 rows affected (0.42 sec)
mysql> insert into db1.t1 values("bob","USA");变长varchar
- 变长: varchar(字符个数)
- 按数据实际大小分配存储空间
- 字符个数超出时，无法写入数据。·大文本类型: text/blob
- 字符数大于65535存储时使用
mysql> create table db1.t7(
-> name char(5),
-> email varchar(30)
-> );
Query OK, 0 rows affected (0.44 sec)
mysql> insert into db1.t7 values("lucy","[email protected]");案例4:
按照如下结构建表:
mysql> desc db1.t3;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name | char(5) | YES | | NULL | |
| mail | varchar(10) | YES | | NULL | |
| homedie | varchar(50) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+1）新建db1库，并切换到db1库
mysql> create database db1;
Query OK, 1 row affected (0.02 sec)
mysql> use db1;
Database changed2）新建t3表
mysql> create table db1.t3(
-> name char(5),
-> mail varchar(10),
-> homedie varchar(50)
-> );
Query OK, 0 rows affected (0.11 sec)3) 查看a3表结构
mysql> desc db1.t3;
+---------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+-------------+------+-----+---------+-------+
| name | char(5) | YES | | NULL | |
| mail | varchar(10) | YES | | NULL | |
| homedie | varchar(50) | YES | | NULL | |
+---------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)4.3、数值型
整数型
只能存储整数
浮点型·浮点型
-格式1∶字段名类型;
-格式2∶字段名类型(总宽度,小数位数)
案例5
要求:按照 下图所示建表
mysql> desc db1.t2;
+---------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+------------+------+-----+---------+-------+
| stu_num | int | YES | | NULL | |
| name | char(5) | YES | | NULL | |
| age | tinyint | YES | | NULL | |
| pay | float | YES | | NULL | |
| money | float(5,2) | YES | | NULL | |
+---------+------------+------+-----+---------+-------+1）创建t2表
mysql> use db1;
Database changed
mysql> create table db1.t2(
-> stu_num int,
-> name char(5),
-> age tinyint,
-> pay float,
-> money float(5,2)
-> );
Query OK, 0 rows affected, 1 warning (0.07 sec)2) 查看t2表结构
mysql> desc db1.t2;
+---------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+---------+------------+------+-----+---------+-------+
| stu_num | int | YES | | NULL | |
| name | char(5) | YES | | NULL | |
| age | tinyint | YES | | NULL | |
| pay | float | YES | | NULL | |
| money | float(5,2) | YES | | NULL | |
+---------+------------+------+-----+---------+-------+
5 rows in set (0.00 sec)4.4、日期时间型
类型
日期时间 datetime
- 范围:1000-01-01 00:00:00 ~ 9999-12-31 23:59:59
- 格式:yyyymmddhhmmss
日期时间 timestamp
- 范围:1970-01-01 00:00:00 ~ 2038-01-19 00:00:00
- 格式:yyyymmddhhmmss
**类型（续1)
日期date**
-范围:0001-01-01 ~ 9999-12-31
-格式:yyyymmdd
年year
-范围:1901~2155
-格式:yyyy
时间time
-格式:HH:MM:SS
类型(续2)
关于日期时间字段
-当未给timestamp字段赋值时，自动以当前系统时间赋值，而datetime值为NULL(空)
year类型
-要求使用4位数赋值
-当使用2位数赋值时:
- 01~69视为 2001~2069
- 70~99视为1970~1999
时间函数
· MySQL服务内置命令
一可以使用时间函数给字段赋值
案例6:
要求:
练习如下时间函数的使用：
now( ) year( ) month( ) day( ) date( ) time( )
curtime( ) curdate( )
按照如下图所示建表
mysql> desc db1.t4;
+------------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+----------+------+-----+---------+-------+
| name | char(10) | YES | | NULL | |
| your_start | year | YES | | NULL | |
| up_time | time | YES | | NULL | |
| birthday | date | YES | | NULL | |
| party | datetime | YES | | NULL | |
+------------+----------+------+-----+---------+-------+1）练习如下命令的使用 now( ) year( ) month( ) day( ) date( ) time( )
mysql> select now(); //使用now()查看当前的日期和时间
+---------------------+
| now() |
+---------------------+
| 2020-11-25 15:18:08 |
+---------------------+
1 row in set (0.00 sec)
mysql> select curdate(); //使用curdate()获得当前的日期
+------------+
| curdate() |
+------------+
| 2020-11-25 |
+------------+
1 row in set (0.00 sec)
mysql> select curtime(); //使用curtime()获得当前的时间
+-----------+
| curtime() |
+-----------+
| 15:18:41 |
+-----------+
1 row in set (0.00 sec)
mysql> select year(now()),month(now()),day(now()); //分别获取当前日期时间中的年份、月份、日
+-------------+--------------+------------+
| year(now()) | month(now()) | day(now()) |
+-------------+--------------+------------+
| 2020 | 11 | 25 |
+-------------+--------------+------------+
1 row in set (0.00 sec)
mysql> select date(now()) ; //获取系统日期
+-------------+
| date(now()) |
+-------------+
| 2020-11-25 |
+-------------+
1 row in set (0.00 sec)
mysql> select date(now());
+-------------+
| date(now()) |
+-------------+
| 2020-11-25 |
+-------------+
1 row in set (0.01 sec)2）创建t4表 建表
mysql> create table db1.t4(
-> name char(10),
-> your_start year,
-> up_time time,
-> birthday date,
-> party datetime
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> desc db1.t4; //查看表结构
+------------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+----------+------+-----+---------+-------+
| name | char(10) | YES | | NULL | |
| your_start | year | YES | | NULL | |
| up_time | time | YES | | NULL | |
| birthday | date | YES | | NULL | |
| party | datetime | YES | | NULL | |
+------------+----------+------+-----+---------+-------+
5 rows in set (0.01 sec)
mysql> insert into db1.t4 values("bob",1990,083000,20191120,20190828200000); //插入记录
Query OK, 1 row affected (0.29 sec)
mysql> insert into db1.t4 values("tom",1991,090000,20191120,now());
Query OK, 1 row affected (0.26 sec)
mysql> select * from db1.t4; //查看表所有列名的集合
+------+------------+----------+------------+---------------------+
| name | your_start | up_time | birthday | party |
+------+------------+----------+------------+---------------------+
| bob | 1990 | 08:30:00 | 2019-11-20 | 2019-08-28 20:00:00 |
| tom | 1991 | 09:00:00 | 2019-11-20 | 2020-11-25 15:37:26 |
+------+------------+----------+------------+---------------------+
2 rows in set (0.00 sec)
mysql> select name from db1.t4; //查看表name列记录
+------+
| name |
+------+
| bob |
| tom |
+------+
2 rows in set (0.00 sec)
mysql> 4.5、枚举型
enum
- enum单选︰
- 格式∶字段名enum(值1，值2,值N)
- 仅能选择一个值
- 字段值必须在列表里选择
set 多选:
-格式:字段名set(值1,值2,值N)
-选择一个或多个值
-字段值必须在列表里选择
案例7:
要示 按照如下图所示建表
mysql> desc db1.t5;
+-------+----------------------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------------------------------+------+-----+---------+-------+
| name | char(5) | YES | | NULL | |
| likes | set('eat','game','film','music') | YES | | NULL | |
| sex | enum('boy','girl','no') | YES | | NULL | |
+-------+----------------------------------+------+-----+---------+-------+1）创建t5表
mysql> create table db1.t5(
-> name char(5),
-> likes set("eat","game","film","music"),
-> sex enum("boy","girl","no")
-> );
Query OK, 0 rows affected (0.30 sec)2）查看表结构
mysql> desc db1.t5;
+-------+----------------------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------------------------------+------+-----+---------+-------+
| name | char(5) | YES | | NULL | |
| likes | set('eat','game','film','music') | YES | | NULL | |
| sex | enum('boy','girl','no') | YES | | NULL | |
+-------+----------------------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)3）插入表记录
mysql> insert into db1.t5 values("bob","eat,film,game","boy");
Query OK, 1 row affected (0.02 sec)
mysql> select * from db1.t5;
+------+---------------+------+
| name | likes | sex |
+------+---------------+------+
| bob | eat,game,film | boy |
+------+---------------+------+
1 row in set (0.00 sec)