What is the difference between Mysqli and Mysql_connect?

The fundamental difference between MySQLi and mysql_connect() lies in the PHP extension they belong to, their feature sets, and their current status within the PHP ecosystem. MySQLi (MySQL Improved Extension) is the modern, feature-rich, and actively maintained extension for interacting with MySQL databases, offering both procedural and object-oriented interfaces. In contrast, mysql_connect() is a specific function from the legacy mysql extension, which has been deprecated and removed from modern PHP versions due to security vulnerabilities and lack of advanced features.

Fundamental Distinction: Extensions vs. Function

To clarify, MySQLi refers to a complete PHP extension that provides a set of functions and classes (e.g., mysqli_connect() for procedural, or new mysqli() for object-oriented) to interact with MySQL. On the other hand, mysql_connect() is just one specific function provided by the older, deprecated mysql extension.

The core distinction, as noted, is that functions starting with mysqli_ (like mysqli_connect()) are designed to work with resources established by the mysqli extension. Conversely, functions starting with mysql_ (like mysql_connect()) operate on resources created by the legacy mysql extension.

Key Differences Summarized

Here's a breakdown of the critical differences between the mysqli extension (which includes mysqli_connect()) and the mysql extension (which includes mysql_connect()):

Feature	MySQLi Extension (e.g., mysqli_connect())	MySQL Extension (e.g., mysql_connect())
Status	Current, actively maintained, and recommended	Deprecated in PHP 5.5, removed in PHP 7.0
API Styles	Supports both Object-Oriented and Procedural	Only Procedural
Prepared Statements	Yes (Crucial for preventing SQL Injection)	No (Directly vulnerable to SQL Injection if not properly escaped)
Stored Procedures	Yes	No
Transactions	Yes	No
Multiple Statements	Yes	No
Security	Higher, with built-in support for prepared statements and robust error handling	Lower, relies heavily on manual input escaping (e.g., mysql_real_escape_string())
Performance	Generally improved due to updated internal architecture	Older architecture, less optimized

As evident, mysqli is the more current version to use and boasts significantly more features compared to its predecessor.

Why MySQLi is the Preferred Choice

• Enhanced Security: The most compelling reason to use mysqli is its support for prepared statements. Prepared statements are a robust way to protect against SQL injection attacks, a common and critical web security vulnerability.
• Richer Feature Set: mysqli provides access to advanced MySQL features such as stored procedures, database transactions, and the ability to execute multiple SQL statements in a single call. These features are essential for building complex and reliable database applications.
• Flexible API: Developers can choose between an intuitive object-oriented interface or a familiar procedural interface, catering to different coding styles and project requirements.
• Active Development & Support: As the officially recommended and actively maintained extension, mysqli receives updates and bug fixes, ensuring compatibility with new PHP and MySQL versions.

Understanding the Deprecation of mysql Extension

The mysql extension, along with its functions like mysql_connect(), was officially deprecated in PHP 5.5.0 and completely removed in PHP 7.0.0. This means that any code relying on mysql_connect() will simply cease to function on modern PHP installations (PHP 7.0 and newer). Projects still using the mysql extension are running on outdated PHP versions, which themselves pose significant security risks and lack performance improvements.

Practical Examples of Connection

To illustrate, here's how connections are typically established with both extensions.

MySQLi (Procedural Style)

<?php
$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "your_database";

// Create connection
$conn = mysqli_connect($servername, $username, $password, $dbname);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully using MySQLi (procedural).";

// Perform database operations...

// Close connection
mysqli_close($conn);
?>

MySQLi (Object-Oriented Style)

<?php
$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "your_database";

// Create connection
$mysqli = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($mysqli->connect_errno) {
    die("Connection failed: " . $mysqli->connect_error);
}
echo "Connected successfully using MySQLi (object-oriented).";

// Perform database operations...

// Close connection
$mysqli->close();
?>

Legacy MySQL (mysql_connect()) - Do Not Use!

<?php
// WARNING: This code is deprecated, insecure, and will NOT run on PHP 7.0 or newer.
// It is provided for historical context only.

$servername = "localhost";
$username = "your_username";
$password = "your_password";
$dbname = "your_database";

// Establish connection
$conn = mysql_connect($servername, $username, $password);

// Check connection
if (!$conn) {
    die("Connection failed: " . mysql_error());
}

// Select the database
$db_selected = mysql_select_db($dbname, $conn);
if (!$db_selected) {
    die("Can't use database: " . mysql_error());
}

echo "Connected successfully using legacy MySQL (procedural).";

// Perform database operations...

// Close connection
mysql_close($conn);
?>

In summary, mysqli is the modern, secure, and feature-rich interface for interacting with MySQL databases in PHP, making the mysql extension and its mysql_connect() function obsolete and dangerous for contemporary web development.