Why does my PHP database connection fail?

PHP database connection fails due to the following reasons: the database server is not running, the host name or port is incorrect, the database credentials are incorrect, or the appropriate permissions are missing. Solutions include: starting the server, checking the hostname and port, verifying credentials, modifying permissions, and adjusting firewall settings.

#Why does my PHP database connection fail?

Introduction

It is common to encounter errors when connecting to a database using PHP. This article describes common problems connecting to databases and their solutions.

Common Errors

• Unable to connect to the MySQL server.
• The host is unreachable.
• Access to the database is denied.

Cause

These errors may have the following causes:

• The database server is not running or is inaccessible.
• The hostname or port is incorrect.
• The database credentials (username, password) are incorrect.
• Lack of appropriate permissions.

Practical case

Error: Unable to connect to the MySQL server.

Cause: The database server is not running.

Solution: Start the MySQL server.

Code sample:

<?php

// 检查 MySQL 服务器是否已启动
$mysqli = new mysqli("localhost", "root", "password");

// 如果连接失败，打印错误信息
if ($mysqli->connect_errno) {
  echo "Failed to connect to MySQL: " . $mysqli->connect_error;
} else {
  echo "Connected to MySQL successfully!";
}

?>

Other solutions

• Host unreachable: Check that the hostname or IP address is correct.
• Access to the database is denied: Check the database credentials and ensure you have the appropriate permissions.
• Lack of appropriate permissions: Modify database user permissions to grant them access to the database.
• Firewall restrictions: Check whether the firewall settings allow communication with the database server.

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