PHP Using PDO and MySQLi Step by step Implementation and Top 10 Questions and Answers
 Last Update:6/1/2025 12:00:00 AM     .NET School AI Teacher - SELECT ANY TEXT TO EXPLANATION.    18 mins read      Difficulty-Level: beginner

PHP Using PDO and MySQLi: A Comprehensive Guide

PHP, being one of the most popular server-side programming languages, comes equipped with several methods for interacting with databases. Among these, PDO (PHP Data Objects) and MySQLi (MySQL Improved) are two of the most widely used extensions. Both PDO and MySQLi offer robust interfaces for interacting with MySQL databases, but they have distinct features and use cases. This guide delves into the details of using these extensions, highlighting their important features and considerations.

What is PDO?

PDO is short for PHP Data Objects. It provides a lightweight, consistent interface for accessing databases in PHP using a single set of functions, regardless of the underlying database being used (MySQL, SQLite, Oracle, etc.). This makes PDO an excellent choice for developers who might be working with multiple database systems.

Key Features of PDO:

  1. Database Abstraction:

    • PDO provides a consistent method of access across different types of databases, which simplifies database switching for applications.
    • This abstraction allows developers to write database-agnostic code, making it more flexible and easier to maintain.

  2. Prepared Statements:

    • PDO supports prepared statements and parameterized queries, which help prevent SQL injection attacks.
    • Prepared statements are used to compile, parse, and optimize SQL queries before execution, enhancing performance and security.

  3. Error Handling:

    • PDO offers flexible error handling methods. You can choose between exceptions or warnings.
    • Handling exceptions using try-catch blocks makes it easier to handle errors gracefully.

  4. Support for Multiple Databases:

    • While our focus is on MySQL, PDO supports 12 different types of databases, which provides immense versatility.

  5. Transactions:

    • PDO supports transaction control (commit, rollback), which is essential for operations that span multiple queries.

What is MySQLi?

MySQLi stands for MySQL Improved. It is an extended database driver for MySQL databases in PHP. MySQLi offers both a procedural and an object-oriented interface, making it highly flexible and suitable for a variety of programming styles.

Key Features of MySQLi:

  1. Procedural and Object-Oriented Interfaces:

    • MySQLi supports both procedural and object-oriented programming styles, allowing developers to choose the style that best fits their needs.
    • This dual approach makes MySQLi a versatile option for both new and experienced developers.

  2. Prepared Statements:

    • Similar to PDO, MySQLi supports prepared statements to prevent SQL injection attacks.
    • It also allows for query execution and fetching results using both procedural and object-oriented styles.

  3. multi-queries:

    • MySQLi supports executing multiple queries in a single statement, which can enhance performance for certain operations.
    • However, caution must be exercised to avoid SQL injection vulnerabilities.

  4. Encryption and Compression:

    • MySQLi supports secure connections through SSL/TLS for data encryption.
    • It also supports compressed data transfer between the client and server, which can improve performance on slow networks.

  5. Enhanced Security Features:

    • MySQLi provides secure by default settings, which make it easier to manage security in your applications.
    • It also integrates well with other security features provided by MySQL.

  6. Transactions:

    • MySQLi supports transaction control (commit, rollback) similar to PDO.

Comparing PDO and MySQLi

When to Use PDO?
  • Cross-Database Support: If your application might need to interact with different types of databases in the future, PDO is the better choice.
  • Simplicity and Consistency: PDO provides a consistent API that simplifies the process of switching between different database systems.
When to Use MySQLi?
  • Flexibility: If you prefer a more flexible approach with both procedural and object-oriented interfaces, MySQLi is the better choice.
  • MySQL-Specific Features: If you are only working with MySQL databases and require specific MySQL features (like multiple queries), MySQLi is ideal.

Code Examples

Here are some code examples to illustrate the usage of PDO and MySQLi.

PDO Example:

try {
    $pdo = new PDO('mysql:host=localhost;dbname=testdb', 'username', 'password');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    
    $stmt = $pdo->prepare('SELECT * FROM users WHERE id = :id');
    $stmt->execute(['id' => 1]);
    
    $user = $stmt->fetch(PDO::FETCH_ASSOC);
    print_r($user);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

MySQLi Example:

Procedural Style:

$mysqli = new mysqli('localhost', 'username', 'password', 'testdb');
if ($mysqli->connect_error) {
    die('Connect Error (' . $mysqli->connect_errno . ') ' . $mysqli->connect_error);
}

$stmt = $mysqli->prepare('SELECT * FROM users WHERE id = ?');
$stmt->bind_param('i', $id);
$id = 1;
$stmt->execute();
$result = $stmt->get_result();
$user = $result->fetch_assoc();
print_r($user);

$stmt->close();
$mysqli->close();

Object-Oriented Style:

$mysqli = new mysqli('localhost', 'username', 'password', 'testdb');
if ($mysqli->connect_error) {
    die('Connect Error (' . $mysqli->connect_errno . ') ' . $mysqli->connect_error);
}

$stmt = $mysqli->prepare('SELECT * FROM users WHERE id = ?');
$stmt->bind_param('i', $id);
$id = 1;
$stmt->execute();
$user = $stmt->fetch_assoc();
print_r($user);

$stmt->close();
$mysqli->close();

Conclusion

Both PDO and MySQLi are powerful extensions for interacting with MySQL databases in PHP. The choice between PDO and MySQLi depends on your specific requirements and preferences. PDO offers a more abstract and database-agnostic approach, making it a great choice for applications that might need to support multiple databases. MySQLi, on the other hand, provides flexibility with both procedural and object-oriented interfaces and is optimized for MySQL databases. Understanding the key features, advantages, and use cases of both extensions will help you make an informed decision based on your project needs.




Examples, Set Route and Run the Application – Data Flow Step-by-Step for Beginners: PHP Using PDO and MySQLi

Introduction

When developing applications using PHP to interact with databases, understanding how to set routes, run the application, and manage data flow is essential. Two of the most commonly used extensions for database interaction in PHP are PDO (PHP Data Objects) and MySQLi (MySQL Improved Extension). In this guide, we'll explore these two methods using practical examples and a step-by-step approach that even beginners can follow.

Setting Up Your Environment

Before diving into coding examples, ensure you have the following prerequisites:

  1. PHP Environment: You may use tools like XAMPP, WAMP, or MAMP which come pre-installed with Apache, MySQL, and PHP.
  2. Database: A MySQL database (or MariaDB) where you will create tables and insert dummy data.
  3. IDE/Text Editor: Visual Studio Code, PhpStorm, or any text editor that suits you.
  4. Basic Knowledge of PHP: Understanding variables, functions, object-oriented programming, etc.

Example: Database Setup

Let's assume we're creating a simple application to manage a list of users using both PDO and MySQLi.

  1. Create a new database:

    CREATE DATABASE simple_app;

  2. Create a users table inside the simple_app database:

    USE simple_app;

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

  3. Insert Dummy Data:

    INSERT INTO users (name, email) VALUES 
('John Doe', 'john@example.com'),
('Jane Smith', 'jane@example.com');

Step-by-Step: Creating a Basic Web Application

Let’s create a simple web application to fetch and display users from our users table using both PDO and MySQLi.

Using PDO (PHP Data Objects)

Step 1: Establish a Database Connection

Create a file named pdo_connect.php:

<?php
try {
    $pdo = new PDO('mysql:host=localhost;dbname=simple_app;charset=utf8mb4', 'root', '');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch (\PDOException $e) {
    throw new \PDOException($e->getMessage(), (int)$e->getCode());
}
?>

Step 2: Create a Route to Fetch Users

Create a file named pdo_get_users.php:

<?php
require 'pdo_connect.php';

$sql = "SELECT * FROM users";
$stmt = $pdo->query($sql);

$users = $stmt->fetchAll(PDO::FETCH_ASSOC);

header('Content-Type: application/json');
echo json_encode($users);
?>

Step 3: Set Route and Run the Application

In your web server configuration (XAMPP, WAMP, etc.), map the path /pdo_get_users to pdo_get_users.php. If you are using the default setup, simply access the script via your browser:

http://localhost/pdo_get_users.php

You’ll see a JSON output listing your users.

Using MySQLi

Step 1: Establish a Database Connection

Create a file named mysqli_connect.php:

<?php
$mysqli = new mysqli("localhost", "root", "", "simple_app");

if ($mysqli->connect_error) {
    die("Connection failed: " . $mysqli->connect_error);
}
?>

Step 2: Create a Route to Fetch Users

Create a file named mysqli_get_users.php:

<?php
require 'mysqli_connect.php';

$sql = "SELECT * FROM users";
$result = $mysqli->query($sql);

$users = array();
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        $users[] = $row;
    }
}

header('Content-Type: application/json');
echo json_encode($users);

$mysqli->close();
?>

Step 3: Set Route and Run the Application

Similarly, map the path /mysqli_get_users to mysqli_get_users.php. Simply access the script via your browser:

http://localhost/mysqli_get_users.php

Again, you’ll see a JSON output listing your users.

Data Flow Overview

  1. Establish Connection:

    • The application starts by establishing a connection to the MySQL database using either PDO or MySQLi.

  2. Generate SQL Query:

    • The PHP script formulates an SQL query to fetch users from the users table.

  3. Execute SQL Query:

    • The query is executed on the MySQL server.

  4. Process Results:

    • Results are fetched from the server and processed in PHP.

  5. Output Data:

    • The processed results are converted to JSON format and sent back to the user as a response.

Conclusion

This example demonstrates a simple way to set up a basic web application using PHP to interact with a MySQL database using both PDO and MySQLi. By following these steps, beginners can understand the fundamentals of database connections, SQL queries, and data handling in PHP. Further explorations might include more complex interactions such as insertions, updates, deletions, and security measures like prepared statements. Happy coding!




Top 10 Questions and Answers on Using PDO and MySQLi with PHP

1. What are PDO and MySQLi?

Answer:
PDO (PHP Data Objects) and MySQLi (MySQL Improved Extension) are both PHP extensions used to connect and interact with MySQL databases. However, they have several key differences:

  • PDO is an abstraction layer that provides a uniform method of accessing multiple databases. While it was initially designed for MySQL, it can also be used with other databases like SQLite, Oracle, etc.
  • MySQLi is a specific extension designed for MySQL. It offers features not available in the older MySQL extension, such as prepared statements, transactions, and support for multiple statements.

Both extensions are built to support secure connections and provide better performance compared to the older MySQL extension.

2. Which one should I use: PDO or MySQLi?

Answer:
Choosing between PDO and MySQLi depends on your project's requirements.

  • Use PDO if: you need to work with different database types beyond MySQL, or want a more object-oriented programming approach. PDO is also easier to switch to other databases if needed, because its syntax tends to be consistent across database systems.
  • Use MySQLi if: you're working exclusively with MySQL databases, performance is critical, and you're familiar with its procedural or object-oriented API. MySQLi can sometimes offer faster access because it is optimized specifically for MySQL.

For most modern projects interacting primarily with MySQL, either tool can suffice, but PDO's flexibility is often a compelling advantage.

3. How do I establish a connection using PDO?

Answer:
Establishing a connection using PDO involves creating a new instance of the PDO class with the DSN (Data Source Name), and optionally passing a username, password, and options array.

try {
    $pdo = new PDO('mysql:host=hostname;dbname=database', 'username', 'password');
    // Set the PDO error mode to exception
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOException $e) {
    echo "Connection failed: " . $e->getMessage();
}

In this example:

  • 'mysql:host=hostname;dbname=database': The DSN indicates the type of database (MySQL), host name, and database name.
  • 'username': Your MySQL user account.
  • 'password': Your MySQL password.
  • Setting the error mode attribute helps in debugging by throwing exceptions.

4. How do I perform a SELECT query using PDO?

Answer:
You can execute SELECT queries with PDO using prepared statements, which help prevent SQL injection attacks.

try {
    $stmt = $pdo->prepare("SELECT * FROM users WHERE id = ?");
    $stmt->execute([$id]); // Use $id value here

    $users = $stmt->fetchAll(PDO::FETCH_ASSOC); // Fetch results as an associative array
    foreach ($users as $user) {
        echo $user['name'] . "<br>";
    }
} catch(PDOException $e) {
    echo "Query failed: " . $e->getMessage();
}

In this code:

  • A prepared statement is created using $pdo->prepare().
  • The execute() method runs the query safely.
  • fetchAll(PDO::FETCH_ASSOC) fetches all rows from the result set as an associative array.

5. How do I execute a SELECT query with MySQLi?

Answer:
Executing SELECT queries with MySQLi can be done either in a procedural or object-oriented style. Here's an example in an object-oriented manner:

$mysqli = new mysqli("hostname", "username", "password", "database");

if ($mysqli->connect_errno) {
    echo "Failed to connect to MySQL: " . $mysqli->connect_error;
    exit();
}

$query = "SELECT * FROM users WHERE id = ?";
$stmt = $mysqli->prepare($query);

$id = 1;
$stmt->bind_param("i", $id); // Bind parameters: i = integer

$stmt->execute();

$result = $stmt->get_result(); // Get the result

while ($row = $result->fetch_assoc()) { // Loop through results
    echo $row['name'] . "<br>";
}

$stmt->close(); // Close statement
$mysqli->close(); // Close connection

This snippet demonstrates:

  • Creating an instance of mysqli for database connection.
  • Preparing and executing a query.
  • Binding query parameters for safety.
  • Fetching and displaying data from the result set.

6. Can I use PDO for transactions?

Answer:
Yes, PDO supports transactions and allows you to control them with ease. You can start, commit, or roll back transactions using methods such as beginTransaction(), commit(), and rollBack().

Example of using PDO for transactions:

try {
    $pdo->beginTransaction();

    $stmt1 = $pdo->prepare("INSERT INTO orders (product_id, quantity) VALUES (:productId, :quantity)");
    $stmt1->execute(['productId' => $productId, 'quantity' => $quantity]);

    $stmt2 = $pdo->prepare("UPDATE products SET stock = stock - :quantity WHERE id = :productId");
    $stmt2->execute(['productId' => $productId, 'quantity' => $quantity]);

    $pdo->commit();
    echo "Transaction completed!";
} catch(PDOException $e) {
    $pdo->rollBack();
    echo "Transaction failed: " . $e->getMessage();
}

This ensures that both insert and update operations are executed successfully or rolled back if any errors occur, maintaining data integrity.

7. Can MySQLi perform transactions?

Answer:
Yes, MySQLi supports transactions as well. The object-oriented interface offers autocommit(), begin_transaction(), commit(), and rollback() methods to manage transactions.

Here's how you can handle transaction with MySQLi:

$mysqli = new mysqli("hostname", "username", "password", "database");

if ($mysqli->connect_errno) {
    echo "Failed to connect to MySQL: " . $mysqli->connect_error;
    exit();
}

try {
    $mysqli->begin_transaction(); // Begin transaction

    $stmt1 = $mysqli->prepare("INSERT INTO orders (product_id, quantity) VALUES (?, ?)");
    $stmt1->bind_param("ii", $productId, $quantity);
    $stmt1->execute();

    $stmt2 = $mysqli->prepare("UPDATE products SET stock = stock - ? WHERE id = ?");
    $stmt2->bind_param("ii", $quantity, $productId);
    $stmt2->execute();

    $mysqli->commit(); // Commit transaction
    echo "Transaction completed!";
} catch(Exception $e) {
    $mysqli->rollback(); // Rollback transaction
    echo "Transaction failed: " . $e->getMessage();
}

$stmt1->close();
$stmt2->close();
$mysqli->close();

This approach is useful when you need to ensure that several related queries succeed together or fail entirely.

8. How do I handle errors in PDO?

Answer:
Handling errors in PDO can be done by setting the error mode attribute (PDO::ATTR_ERRMODE). You can choose between three modes:

  • PDO::ERRMODE_SILENT: Standard silent mode (default). PDO will only set the error code (errorInfo[]) and errorCode() methods return.
  • PDO::ERRMODE_WARNING: Issue E_WARNING for everything but PDO::ATTR_ERRMODE_SILENT.
  • PDO::ERRMODE_EXCEPTION: Throw an exception whenever an error occurs.

Here’s how to set error handling to exception mode and handle exceptions:

try {
    $pdo = new PDO('mysql:host=hostname;dbname=database', 'username', 'password');
    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); // Set error handling

    $stmt = $pdo->prepare("SELECT * FROM nonexistent_table");
    $stmt->execute();
} catch(PDOException $e) {
    echo "Error: " . $e->getMessage();
}

Setting the error mode to PDO::ERRMODE_EXCEPTION makes it easy to catch and display errors.

9. How do I handle errors in MySQLi?

Answer:
Error handling in MySQLi can be managed via checking specific methods or enabling warnings.

  • Procedural Style:
$link = mysqli_connect("hostname", "username", "password", "database");

if (!$link) {
    die("Connect failed: " . mysqli_connect_error());
}

$result = mysqli_query($link, "SELECT * FROM nonexistent_table");
if (!$result) {
    echo "Query failed: " . mysqli_error($link);
} else {
    while($row = mysqli_fetch_assoc($result)) {
        echo $row['name'] . "<br>";
    }
}

mysqli_close($link);
  • Object-Oriented Style:
$mysqli = new mysqli("hostname", "username", "password", "database");

if ($mysqli->connect_error) {
    die("Connect failed: " . $mysqli->connect_error);
}

$query = "SELECT * FROM nonexistent_table";
if (!$result = $mysqli->query($query)) {
    echo "Query failed: " . $mysqli->error;
} else {
    while($row = $result->fetch_assoc()) {
        echo $row['name'] . "<br>";
    }
    $result->close();
}

$mysqli->close();

Here, errors are checked immediately after the connection attempt and after each query execution.

10. What are the advantages of using prepared statements?

Answer:
Prepared statements are a powerful feature in both PDO and MySQLi that offer several advantages:

  • Security: By separating SQL logic from the actual data, prepared statements help prevent SQL injection attacks.
  • Performance: Prepared statements are parsed once and executed multiple times, which can be more efficient than parsing every time a query is run.
  • Simplicity and Maintainability: Code becomes cleaner by reusing query structures and varying only the parameter values. This makes the code easier to maintain and less prone to errors.
  • Flexibility: With PDO's support for multiple database systems, prepared statements enhance portability across platforms.

To write a prepared statement in PDO:

$stmt = $pdo->prepare("SELECT * FROM users WHERE id = :userId");
$stmt->execute(['userId' => $userId]);
$user = $stmt->fetch(PDO::FETCH_ASSOC);

And in MySQLi (object-oriented):

$stmt = $mysqli->prepare("SELECT * FROM users WHERE id = ?");
$stmt->bind_param("i", $userId);
$stmt->execute();
$result = $stmt->get_result();
$user = $result->fetch_assoc();

Both snippets illustrate the preparation of a SQL statement, execution with safely bound parameters, and fetching the results.

Conclusion

While both PDO and MySQLi offer robust solutions for interacting with MySQL databases in PHP, your choice largely depends on the specific needs of your project. If you are planning to work with multiple types of databases or prefer an object-oriented approach, PDO is a great option. For applications that require high throughput and maximum performance with MySQL specifically, MySQLi might be the better choice. Regardless of the extension, leveraging features like prepared statements and proper error handling is crucial for building secure and maintainable applications.