MySQL Brief Explanation

MySQL

• MySQL is the name of a database
• A better database that works with PHP
• The front end asks for data from the back end, and the back end queries the data in the database and returns it to the front end
• Next, let’s talk about using PHP to manipulate the database

MySQL 是最流行的关系型数据库管理系统（非关系型数据库简略介绍）
关系数据库管理系统(Relational Database Management System)的特点
1.数据以表格的形式出现
2.每行为各种记录名称
3.许多的行和列组成一张表单
4.若干的表单组成database
5.主键：主键是唯一的。一个数据表中只能包含一个主键。你可以使用主键来查询数据。

Data type of the database

• Numerical type

Types of	size	description
tinyint	1 byte	Small integer value
smallint	2 bytes	Large integer value
mediumint	3 bytes	Large integer value
int or integer	4 bytes	Large integer value
bigint	8 bytes	Very large integer value
float	4 bytes	Single-precision floating-point value
double	8 bytes	Double-precision floating-point value
decimal		Decimal value

• Date and time type

Types of	format	description
DATE (date)	YYYY-MM-DD	Date value
TIME(time)	HH:MM:SS	Time value or duration
YEAR(year)	YYYY	Year value
DATETIME(datetime)	YYYY-MM-DD HH:MM:SS	Mixed date and time values
TIMESTAMP(timestamp)	YYYYMMDD HHMMSS	Timestamp

• String type

Types of	size	description
CHAR(char)	0-255 bytes	Fixed-length string
VARCHAR(varchar)	0-65535 bytes	Variable length string
TINYBLOB (tinyblob)	0-255 bytes	Binary string of no more than 255 characters
TINYTEXT (tinytext)	0-255 bytes	Short text string
BLOB(blob)	0-65 535 bytes	Long text data in binary form
TEXT(text)	0-65 535 bytes	Long text data
MEDIUMBLOB(mediumblob)	0-16 777 215 bytes	Medium-length text data in binary form
MEDIUMTEXT(mediumtext)	0-16 777 215 bytes	Medium-length text data
LONGBLOB(longblob)	0-4 294 967 295 bytes	Very large text data in binary form
LONGTEXT (longtext)	0-4 294 967 295 bytes	Very large text data

PHP operating database

• Previously, it was a simple understanding of the database, you don’t need to memorize it all, just understand it.
• Next, we are to use php to link to the mysql database to add, delete, modify and check data
• To operate the database, in addition to the php syntax, a mysql sql statement is also required
• Steps to use php to manipulate the database
  1. Establish a link with the database
  2. Use sql statement to operate the database
  3. Get results
  4. The link to the database is broken

Establish a link with the database

• php5 syntax:
  • mysql_connect('ip地址','数据库用户名','数据库密码')
  • mysql_select_db('你要操作的小仓库名称')
• php7 syntax:
  • mysqli_connect('ip地址','数据库用户名','数据库密码','你要操作的小仓库名称')

<?php
	$link = mysqli_connect('127.0.0.1','root','root','student');
?>

-我们有了链接信息`$link`以后就可以继续操作数据库了

Execute SQL statement

• php5 syntax:

  • mysql_query('你要执行的sql语法',连接信息)

• php7 syntax:

  • mysqli_query(连接信息,'你要执行的sql语法')

<?php
	
	# 避免中文乱码
	mysqli_query($link,"set names utf8");
	# 下面就是使用SQL语句对数据库进行操作
	$res = mysqli_query($link,"SELECT * FROM student");
?>

Analytical data

• php5 syntax:
  • 解析本行数据:mysqli_fetch_assoc(要解析的数据);
  • 没有解析全部结果的方法
• php7 syntax:
  • 解析本行数据:mysqli_fetch_assoc(要解析的数据);
  • 解析所有数据:mysqli_fetch_all(要解析的数据,MYSQLI_ASSOC);

<?php
	# 解析所有行的数据
	$arr = mysqli_fetch_all($res,MYSQLI_ASSOC);
	# 转json查看获取到的结果
	print_r(json_encode($arr));
?>

Close link

• After all is used up, we'd better close the database link

• php5 syntax:

  • mysql_close(链接信息);

• php7 syntax:

  • mysqli_close(链接信息);

<?php
	mysqli_close($link);
?>

Complete steps

• Let's write the complete steps of the operation

<?php
	$link = mysqli_connect('127.0.0.1','root','root','student');
	mysqli_query($link,"set names utf8");
	$res = mysqli_query($link,"SELECT * FROM student");
	$arr = mysqli_fetch_all($res,MYSQLI_ASSOC);
	print_r(json_encode($arr));
	mysqli_close($link);
?>

Commonly used SQL statements

• I just said how to operate the database
• Now we learn about SQL statements commonly used when operating a database
• We rely on these sql statements for database operations

check sentence

<?php
  # 查询 student 这个表里面的所有数据
  $sql = 'SELECT * FROM `student`';
    
  # 查询 student 表中的数据里面 gender 为 男 的数据
  $sql = 'SELECT * FROM `student` WHERE `gender`="男"';
    
  # 查询 student 表中的数据里面 age 大于 18 的数据
  $sql = 'SELECT * FROM `student` WHERE `age`>18';
    
  # 查询 student 表中的数据里面 age 大于 18 且 gender 为 男 的数据
  $sql = 'SELECT * FROM `student` WHERE `age`>18 AND `gender`="男"';

  # 查询 student 表中的数据里面 age 小于 22 或者 age 大于 28 的数据
  $sql = 'SELECT * FROM `student` WHERE `age`<22 OR `age`>28';

  # 查询 student 表中的数据里面从 第几条开始 查询多少条
  $sql = 'SELECT * FROM `student` LIMIT 0, 10';
    
  # 先按照条件筛选出数据以后再进行分页查询
  # 下面是查询表中所有 age>18 且 性别为男的所有数据，查出来以后从第 10 条开始查 10 条
  $sql = 'SELECT * FROM `student` WHERE `age`>18 AND `gender`="男" LIMIT 10, 10';

  # 查询表的模糊查询
  # 下面表示查询表中所有数据里面 name 字段中包含 "三" 字的数据
  $sql = 'SELECT * FROM `student` WHERE `name` LIKE "%三%"';

  # 查询排序，查询的时候按照某一个字段升序或降序排序
  $sql = 'SELECT * FROM `student` ORDER BY `age` ASC';
  $sql = 'SELECT * FROM `student` ORDER BY `age` DESC';
?>

Add sentence

<?php
  # 向表中增加一条数据，再增加的时候主键不能由我们书写，而是 mysql 数据库自己递增
  $sql = 'INSERT INTO `student` VALUES(null, "张三", 18, "男", 1913, 100)';
    
  # 插入固定几个键的数据，其他的用默认值
  $sql = 'INSERT INTO `student` (`name`, `age`) VALUES("李四", 22)';
?>

Delete statement

<?php
  # 删除表中 id 为 100 的数据
  $sql = 'DELETE FROM `student` WHERE `id`=100';

  # 删除表中 name 为 张三 的数据
  $sql = 'DELETE FROM `student` WHERE `name`="张三"'
?>

Modify the statement

<?php
  # 更新一条 id 为 100 的数据中的 name 字段的值和 age 字段的值
  $sql = 'UPDATE `student` SET `name`="张三", `age`=10 WHERE `id`=100'
    
  # 更新数据的时候让所有的数据增加一些内容
  $sql = 'UPDATE `student` SET `age`=age+1'
?>