##Detailed explanation of the relationship between Apache, PHP and Mysql

Learning method

Clearing the relationship between Apache, PHP and MySQL is very helpful for beginners to understand the running process of the program. To learn a new thing, you must understand The three most basic questions: what, what, and why.

What refers to the macro-level functional description of new things

What is Apache? It is a web server that can provide Http services.

What does Apache have? Apache has a virtual host function, different working modes (MPM mode), logging function, compression function, various functional modules, etc.

ApacheWhy? Why do you need to use Apache? In what scenarios is Apache suitable to be used? What scenarios are not suitable for use? Can other web servers be used instead? Apache can call the PHP interpreter to work. Can it work with other script interpreters?

Basic understanding of Apache, PHP and Mysql

Apache is a Web server: providing data to the outside based on protocols such as Http/Https/Websocket , file acquisition function.

PHP is a programmable scripting language: It provides basic computing and logical processing functions, and can be well applied to the development of Web website functional requirements.

MySQL is a relational database: a tool for storing, modifying, retrieving and managing data. The database can be managed through Structured Query Language (SQL).

The relationship between Apache and PHP

The relationship between Apache and the PHP interpreter, It is the relationship between calling and being called. Apache actively calls the PHP interpreter to execute the PHP script file, and the PHP interpreter is called by Apache.

Apache is web server software. It can accept requests from clients through protocols such as Http/Https. When the requested file is a PHP script file, it will call the PHP interpreter to interpret and execute the script. content, and encapsulates the results returned by the interpreter into data in the corresponding format according to the corresponding protocol rules, and then returns the data to the requesting client.

How PHP is called by Apache, you can refer to the fourth section "Detailed explanation of PHP's operating mode Sapi", or the next section "Detailed explanation of Apache's MPM and the PHP mode adopted"

The relationship between PHP and MySql

The relationship between PHP and Mysql is also the relationship between calling and being called. PHP calls Mysql through SQL language For the management function of the database, the Mysql database always passively accepts operation instructions.

MYSQL is a small relational database software. It provides database support for various software. Mysql can be operated through PHP. Similarly, Mysql can also be operated using other languages. Similarly, PHP can also operate other databases, not necessarily It's MYSQL.

How does PHP call Mysql database to operate?

The language rule used for interaction between PHP and Mysql is SQL, but PHP and Mysql are two independent applications. If you want to interact, you must first establish a connection, just like a browser accessing a Web server, before requesting data You also need to successfully establish a tcp connection before sending.

The process of establishing a connection between a PHP script and Mysql is completed by PHP's Mysqld/PDO and other drivers. The essence of these drivers are PHP modules, that is, a collection of related functions that can be recognized by the PHP interpreter. Generally, Written in C language.

For the PHP language, it shields the detailed process of specific connection establishment and database protocol operations, and exposes some basic interfaces to the PHP language, that is, some database operation functions that PHP can call, such as connecting to the database, Execute database SQL commands, disconnect, etc.

In short, the process of PHP calling the Mysql database is usually operated through the PHP database driver module. Its essence is also a network data request operation (follow the MySql communication protocol to establish a connection, use SQL syntax to execute specific operational instructions).

Running environment of Apache, PHP and Mysql

To use a PHP program, you need to build a PHP first The running environment of PHP is the environment that contains the three softwares of PHP, Apache and Mysql. The conditions that need to be met are that Apache can call the PHP interpreter to execute PHP scripts, and PHP can connect to the Mysql database to operate and manage the stored data. When the above two conditions are met, the running environment of Apache, PHP and Mysql is a complete PHP running environment.

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