The relationship between sql and php
1: SQL
Structured Query Language (SQL), referred to as SQL, is a special-purpose programming language. It is a database query and programming language used to access data and query, update and manage relational database systems.
Structured Query Language is a high-level, non-procedural programming language that allows users to work on high-level data structures. It does not require users to specify the data storage method, nor does it require users to understand the specific data storage method, so different database systems with completely different underlying structures can use the same structured query language as the interface for data input and management. Structured Query Language statements can be nested, which makes it extremely flexible and powerful.
2: mysql
MySQL is a relational database management system developed by the Swedish MySQL AB company and is currently a product of Oracle. MySQL is one of the most popular relational database management systems. In terms of WEB applications, MySQL is one of the best RDBMS (Relational Database Management System) application software.
MySQL is a relational database management system. A relational database stores data in different tables instead of putting all data in one large warehouse, which increases speed and flexibility.
The SQL language used by MySQL is the most commonly used standardized language for accessing databases. MySQL software adopts a dual licensing policy and is divided into community version and commercial version. Due to its small size, fast speed, low total cost of ownership, and especially the characteristics of open source, MySQL is generally chosen as the website database for the development of small and medium-sized websites.
Due to the excellent performance of its community version, it can form a good development environment with PHP and Apache.
2: PHP
PHP (full name: PHP: Hypertext Preprocessor, that is, "PHP: Hypertext Preprocessor") is an open source general-purpose computer scripting language , especially suitable for web development and can be embedded in HTML. The syntax of PHP draws on the characteristics of popular computer languages such as C language, Java and Perl, making it easy for ordinary programmers to learn. The main goal of PHP is to allow web developers to quickly write dynamic pages, but PHP is also used in many other areas.
PHP has a wide range of applications, especially in the development of web programs. Generally speaking, PHP is mostly run on a web server, and the web pages browsed by users are generated by running PHP code. PHP can run on most servers and operating systems, and using PHP is completely free.
In short:
PHP is a general computer scripting language, that is, a logic language, and SQL language is the most commonly used standardized language for accessing databases, then PHP uses logic to go to the database to call the data that the customer wants to see.
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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。

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。

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。

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。

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。

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。


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