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🗣 Wd提问: mysqli_connect

🤖 Ai回答:
`mysqli_connect()` is a PHP function used to open a new connection to a MySQL database server、It's part of the MySQLi (MySQL Improved) extension, which provides an interface for interacting with MySQL databases.

Basic Syntax

php
mysqli_connect($hostname, $username, $password, $database, $port, $socket);

Parameters

| Parameter | Description | Required |

| `$hostname` | MySQL server host (e.g., localhost, 127.0.0.1) | Yes |
| `$username` | MySQL username | Yes |
| `$password` | MySQL password | Yes |
| `$database` | Default database to select | No |
| `$port` | Port number (default: 3306) | No |
| `$socket` | Socket or named pipe to use | No |

Examples

Basic Connection
php
<?php
$connection = mysqli_connect(localhost, username, password);

if (!$connection) {
die(Connection failed: 、mysqli_connect_error());
}
echo Connected successfully!;
?

Connection with Database Selection
php
<?php
$connection = mysqli_connect(localhost, username, password, my_database);

if (!$connection) {
die(Connection failed: 、mysqli_connect_error());
}
echo Connected successfully to database!;
?

Connection with Custom Port
php
<?php
$connection = mysqli_connect(localhost, username, password, my_database, 3307);

if (!$connection) {
die(Connection failed: 、mysqli_connect_error());
}
?

Error Handling

Always check if the connection was successful:

php
<?php
$connection = mysqli_connect(localhost, username, password, database);

// Check connection
if (mysqli_connect_errno()) {
echo Failed to connect to MySQL: 、mysqli_connect_error();
exit();
}
?

Alternative: Object-Oriented Style

You can also use the object-oriented approach:

php
<?php
$mysqli = new mysqli(localhost, username, password, database);

// Check connection
if ($mysqli-connect_errno) {
echo Failed to connect to MySQL: 、$mysqli-connect_error;
exit();
}
?

Closing the Connection

While PHP automatically closes connections when the script ends, it's good practice to close them explicitly:

php
<?php
$connection = mysqli_connect(localhost, username, password, database);

// Your database operations here...

// Close connection
mysqli_close($connection);
?

Important Notes

1、Security: Never hardcode credentials in your code、Use environment variables or configuration files outside the web root.

2、Error Reporting: In production, avoid displaying detailed error messages to users.

3、Persistent Connections: Add `p:` prefix to hostname for persistent connections:
php
$connection = mysqli_connect(p:localhost, username, password);

4、Deprecated: The old `mysql_connect()` function is deprecated and removed in PHP 7.0+、Always use MySQLi or PDO.

Best Practice Example

php
<?php
// Configuration (ideally from environment variables)
$host = $_ENV['DB_HOST'] ?? 'localhost';
$username = $_ENV['DB_USER'] ?? 'root';
$password = $_ENV['DB_PASS'] ?? '';
$database = $_ENV['DB_NAME'] ?? 'myapp';

// Create connection
$connection = mysqli_connect($host, $username, $password, $database);

// Check connection
if (!$connection) {
// Log error instead of displaying to user in production
error_log(Database connection failed: 、mysqli_connect_error());
die(Sorry, we're experiencing technical difficulties.);
}

// Set charset to prevent SQL injection issues
mysqli_set_charset($connection, utf8mb4);

// Your application logic here...

// Close connection when done
mysqli_close($connection);
?

This function is essential for any PHP application that needs to interact with a MySQL database.

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