


Infinite classification is a data structure often used in actual development, generally we call it a tree structure.
Title design: Similar to Taobao product classification, you can set its subcategories in any category.
1. Create `type` data table
`id` self-increase
`fid` int(11) default (0), parent Node id
`name` varchar(50), category name
CREATE TABLE ` type` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`fid` int(11) NOT NULL DEFAULT '0',
`name` varchar(50) NOT NULL,
PRIMARY KEY (`id`)
)
2. Add
Let’s first add a few top-level categories
INSERT INTO `type` (`id`, `fid`, `name`) VALUES (NULL, '0', 'Mobile phone' );
INSERT INTO `type` (`id`, `fid`, `name`) VALUES (NULL, '0', 'Computer');
INSERT INTO `type` (`id`, ` fid`, `name`) VALUES (NULL, '0', 'shoes');
INSERT INTO `type` (`id`, `fid`, `name`) VALUES (NULL, '0', ' Clothes');
Here fid=0 represents the top category
Then we add several sub-categories for {computer}
INSERT INTO `type` (`id`, `fid`, `name`) VALUES (NULL, '2', 'Desktop') , (NULL, '2', 'notebook');
Here fid=2, the id 2 is the id of the category {Computer}, if you add a subcategory of {Shoes}, then fid= 3
Similarly, if we add a subcategory for {notebook}, fid=6
INSERT INTO `type` (`id`, `fid`, `name`) VALUES (NULL, '6', 'ausu'), (NULL, '6', 'hp');
3. Delete
If we want to delete the category {Notebook}, it is very simple
DELETE FROM `type` WHERE `id`=6
We must also remember to handle the subcategory of {notebook} accordingly
function del($fid) {
$sql="SELECT * FROM `type` WHERE `fid`=$ fid";
$rs=mysql_query($sql);
for ($i = 0; $i $sql="DELETE FROM `type` WHERE `id`={$rs[$i]['id']}";
mysql_query($sql);
del($rs['id']); //Recursion
}
}
del(6);//Execute the operation
Here you may wonder why it is so troublesome to use recursion instead of deleting directly like this
DELETE FROM `type` WHERE `fid`=6
In this way, can’t we delete {ausu} and {hp} directly? But assuming {ausu} has a subcategory {a1}, and {a1} also has a subcategory {a2}, we cannot completely delete the data without recursion.
3. Search
1. Find the subcategory of {Computer}
SELECT * FROM `type` WHERE `fid`=2
2. Find all subcategories of {Computer}
function sel($fid) {
$sql="SELECT * FROM `type` WHERE `fid`=$fid";
$rs=mysql_query($sql);
for ($i = 0; $i echo $rs[$i]['name'];
sel($rs[$i]['id']);//Recursion
}
}
sel(2);
4. Actual data application
Add a field `tid` in the data table, and the field value is the id of the `type` table of the category to which the record belongs. It must be id and not name, because the value of name may change.
For example, query the products belonging to the {Computer} category
SELECT * FROM `goods` WHERE `tid`=2
Note: The code may not be run before, but there may be errors, but the idea is correct. The main thing is to understand the tree structure, and Not memorizing code.

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

DVWA
Damn Vulnerable Web App (DVWA) is a PHP/MySQL web application that is very vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, to help web developers better understand the process of securing web applications, and to help teachers/students teach/learn in a classroom environment Web application security. The goal of DVWA is to practice some of the most common web vulnerabilities through a simple and straightforward interface, with varying degrees of difficulty. Please note that this software

SublimeText3 English version
Recommended: Win version, supports code prompts!

ZendStudio 13.5.1 Mac
Powerful PHP integrated development environment
