python web开发 MySQL数据库基础

文章目录

- 1. 简介
- 2. 下载安装
- 3. 操作 MysQL 数据库
- - 3.1 创建数据库
  - 3.2 选择数据库
  - 3.3 查看数据库
  - 3.4 删除数据库
- 4. 数据类型
- 5. 操作 MysQL 数据表
- - 5.1 创建数据表
  - 5.2 查看表的结构
  - 5.3 修改表的结构
  - 5.4 删除数据表
- 6. 操作 MySQL 数据表记录
- - 6.1 添加数据
  - 6.2 查询、修改、删除

learning from 《python web开发从入门到精通》

1. 简介

MySQL 是目前最为流行的开源数据库，网络化、跨平台的关系型数据库
特点：功能强大（多种引擎），跨平台，速度快（B树磁盘表+索引压缩），免费，支持多种语言，存储容量大（由外部操作系统对文件大小的限制决定）

2. 下载安装

跳过登录，下载 (mysql-installer-community-8.0.27.1.msi) 470MB：https://dev.mysql.com/downloads/

下载慢？使用清华源 https://mirrors.tuna.tsinghua.edu.cn/
点击它：https://mirrors.tuna.tsinghua.edu.cn/mysql/downloads/MySQLInstaller/mysql-installer-community-8.0.27.1.msi

我选的 Full 全量安装，添加 path 环境变量 C:\Program Files\MySQL\MySQL Server 8.0\bin

mysql -u root -p，再输入安装时设置的密码就可以进入了

> mysql -u root -p
Enter password: ******
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 21
Server version: 8.0.27 MySQL Community Server - GPLCopyright (c) 2000, 2021, Oracle and/or its affiliates.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. 操作 MysQL 数据库

3.1 创建数据库

create database DBname;

mysql> create database michaeldata;
Query OK, 1 row affected (0.05 sec)

表名，不能重名

mysql> create database michaeldata;
ERROR 1007 (HY000): Can't create database 'michaeldata'; database exists

可以是字母，阿拉伯数字，下划线，$ ，中的任意字符开头，但不能是纯数字，名称最长64个字符，别名最多256个字符
不能是内置的关键字
各平台间的表名大小写敏感度不一样，建议都用小写表名

mysql> create database 123data;
Query OK, 1 row affected (0.03 sec)mysql> create database $;
Query OK, 1 row affected (0.04 sec)mysql> create database 123;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '123' at line 1

# window 大小写不敏感
mysql> create database michaeldatA;
ERROR 1007 (HY000): Can't create database 'michaeldata'; database exists

3.2 选择数据库

use DBname;

mysql> use michaeldata;
Database changed

显示当前数据库

select database();

mysql> select database();
+-------------+
| database()  |
+-------------+
| michaeldata |
+-------------+
1 row in set (0.00 sec)

3.3 查看数据库

show databases;已经存在的数据库

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| $                  |
| 123data            |
| information_schema |
| michaeldata        |
| mysql              |
| performance_schema |
| sakila             |
| sys                |
| world              |
+--------------------+
9 rows in set (0.02 sec)

3.4 删除数据库

drop database DBname;(慎重，没有备份是恢复不了的)

mysql> drop database $;
Query OK, 0 rows affected (0.04 sec)mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| 123data            |
| information_schema |
| michaeldata        |
| mysql              |
| performance_schema |
| sakila             |
| sys                |
| world              |
+--------------------+
8 rows in set (0.00 sec)

4. 数据类型

数字

TINYINT，SMALLINT，MEDIUMINT，INT，BIGINT

字符串

普通文本：CHAR，VARCHAR（后者长度可变）
TEXT适合存储长文本，BLOB适合存储二进制数据（文本，声音，图像）
两者也可以带前缀 tiny，medium，long，对应范围不同
ENUM枚举，SET一组值

日期和时间

DATETIME，DATE，TIMESTAMP，TIME，TEAR，如果赋值不合法，会被0代替

5. 操作 MysQL 数据表

5.1 创建数据表

CREATE TABLE table_name (column_name column_type);

mysql> create table users(-> id int(8) auto_increment primary key,-> username varchar(30) not null,-> password varchar(30) not null,-> createtime datetime);
Query OK, 0 rows affected, 1 warning (0.08 sec)

在这里插入图片描述

5.2 查看表的结构

show columns from 数据库.数据表;

mysql> show columns from users;
+------------+-------------+------+-----+---------+----------------+
| Field      | Type        | Null | Key | Default | Extra          |
+------------+-------------+------+-----+---------+----------------+
| id         | int         | NO   | PRI | NULL    | auto_increment |
| username   | varchar(30) | NO   |     | NULL    |                |
| password   | varchar(30) | NO   |     | NULL    |                |
| createtime | datetime    | YES  |     | NULL    |                |
+------------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)
4 rows in set (0.00 sec)

describe 表名;可简写为 desc 表名，也可只看某列（后面加列名）

mysql> describe users; 
+------------+-------------+------+-----+---------+----------------+
| Field      | Type        | Null | Key | Default | Extra          |
+------------+-------------+------+-----+---------+----------------+
| id         | int         | NO   | PRI | NULL    | auto_increment |
| username   | varchar(30) | NO   |     | NULL    |                |
| password   | varchar(30) | NO   |     | NULL    |                |
| createtime | datetime    | YES  |     | NULL    |                |
+------------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

mysql> desc users createtime;
+------------+----------+------+-----+---------+-------+
| Field      | Type     | Null | Key | Default | Extra |
+------------+----------+------+-----+---------+-------+
| createtime | datetime | YES  |     | NULL    |       |
+------------+----------+------+-----+---------+-------+
1 row in set (0.00 sec)

5.3 修改表的结构

alter table 表名 alter_spec[,alter_spec]

可参考：https://www.w3cschool.cn/mysql/mysql-alter.html

例如，添加新字段 address，更改 username 为 varchar(50)

ALTER TABLE users
add address varchar(52) not null,
modify username varchar(50)

mysql> desc users;
+------------+-------------+------+-----+---------+----------------+
| Field      | Type        | Null | Key | Default | Extra          |
+------------+-------------+------+-----+---------+----------------+
| id         | int         | NO   | PRI | NULL    | auto_increment |
| username   | varchar(50) | YES  |     | NULL    |                |
| password   | varchar(30) | NO   |     | NULL    |                |
| createtime | datetime    | YES  |     | NULL    |                |
| address    | varchar(52) | NO   |     | NULL    |                |
+------------+-------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

5.4 删除数据表

drop table 表名;

mysql> create table temp(id int);
Query OK, 0 rows affected (0.09 sec)mysql> drop table temp;
Query OK, 0 rows affected (0.05 sec)

避免报错 if exists

mysql> drop table temp;
ERROR 1051 (42S02): Unknown table 'michaeldata.temp'mysql> drop table if exists temp;
Query OK, 0 rows affected, 1 warning (0.03 sec)

6. 操作 MySQL 数据表记录

6.1 添加数据

mysql> insert into users(id, username, password, createtime, address)-> values (1, 'michael', '123', '2021-12-01 00:00:10', 'China');
Query OK, 1 row affected (0.03 sec)

mysql> select * from users;
+----+----------+----------+---------------------+---------+
| id | username | password | createtime          | address |
+----+----------+----------+---------------------+---------+
|  1 | michael  | 123      | 2021-12-01 00:00:10 | China   |
+----+----------+----------+---------------------+---------+
1 row in set (0.00 sec)

如果是全部列的数据都有，可以省略列名

mysql> insert into users-> values (3, 'happy', '456', '2021-12-01 15:14:10', 'China');
Query OK, 1 row affected (0.03 sec)mysql> select * from users;
+----+----------+----------+---------------------+---------+
| id | username | password | createtime          | address |
+----+----------+----------+---------------------+---------+
|  1 | michael  | 123      | 2021-12-01 00:00:10 | China   |
|  3 | happy    | 456      | 2021-12-01 15:14:10 | China   |
+----+----------+----------+---------------------+---------+
2 rows in set (0.00 sec)

mysql> insert into users(id, username, password, address)-> values (4, 'bird', '789', 'China');
Query OK, 1 row affected (0.04 sec)mysql> select * from users;
+----+----------+----------+---------------------+---------+
| id | username | password | createtime          | address |
+----+----------+----------+---------------------+---------+
|  1 | michael  | 123      | 2021-12-01 00:00:10 | China   |
|  3 | happy    | 456      | 2021-12-01 15:14:10 | China   |
|  4 | bird     | 789      | NULL                | China   |
+----+----------+----------+---------------------+---------+
3 rows in set (0.00 sec)