What is the reason why php fails to connect to mysql? How to deal with it?

In website development, PHP and MySQL are two essential technologies. As a server-side language, PHP can complete many website functions through interaction with the database, while MySQL is a powerful database management system. However, during the actual development process, we will also encounter connection failures when PHP connects to MySQL. This article describes possible causes of connection failure and provides solutions.

1. PHP extension is not installed or loaded

Connect to the MySQL database through mysqli or PDO in PHP. However, during the default PHP installation process, these extensions are not automatically installed. If we do not install or load the MySQL extension, it will cause failure to connect to MySQL.

Solution:

Check whether the MySQL extension is enabled in the php.ini configuration file. You can search for extension=mysqli.so or extension=pdo_mysql.so statements to check. If not, you will need to manually install or load the MySQL extension.

2. MySQL service is not started

Another possible reason for failure to connect to MySQL is that the MySQL service is not started. After technical operation and maintenance personnel make modifications to the system, the MySQL service may stop running and the database cannot be connected.

Solution:

Confirm whether the MySQL service is started by checking the MySQL log or command line. In Windows systems, you can check whether the MySQL service is running by going to "Services". In Linux or MacOS systems, you can enter sudo service mysql status or systemctl status mariadb or mysqld service through the command line to check whether the MySQL service is running normally.

3. MySQL username and password are incorrect

If the username or password of the MySQL server is incorrect, the connection will fail. This may be due to an error during the development phase, or due to an inconsistency between the deployment environment and the development environment.

Solution:

Make sure the MySQL username and password are correct. You can try to connect to MySQL through the command line to test whether the username and password are correct.

4. Insufficient MySQL access rights

MySQL can grant different access rights to different users. If the user name used to connect to MySQL does not have sufficient permissions, the connection will fail.

Solution:

Check whether the user name connected to MySQL has sufficient access rights. You can view the user's permissions by typing show grants for user@hostname on the command line. If the permissions are insufficient, you can grant the user more permissions through the GRANT statement.

Summary:

The above are the common causes and solutions for MySQL connection failure. During the development phase and deployment environment, if you find that the MySQL connection fails, you can solve the problem by checking these aspects.

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