PHP Interview Questions

PHP remains one of the core building blocks of web-based software. Thanks to its ability to generate dynamic content, handle backend operations, manage databases, and support frameworks, it is still widely used in large-scale projects.

In this article, we’ll explore the most up-to-date and popular PHP interview questions, including topics like Laravel, WordPress, MySQL, performance, and frameworks, with example answers and code snippets.

Whether you're a junior, mid-level, or senior backend developer candidate, the following technical topics can set you apart during interviews.

1. What is PHP? What Role Does It Play on the Server Side?

• PHP (Hypertext Preprocessor) is a server-side, open-source scripting language that generates dynamic content.
• PHP files run on the server and send the result as HTML output to the client (browser).

Quick Facts:

• PHP is interpreted, not compiled
• Can be embedded into HTML
• Works with web servers like Apache, NGINX, and IIS

Sample Code – Basic PHP File:

<?php
echo "Hello, Techcareer!";
?>

2. Popular PHP Interview Questions: Data Types & Variables

What are the data types in PHP?

• String
• Integer
• Float (Double)
• Boolean
• Array
• Object
• NULL
• Resource

Example:

<?php
$name = "Ali";     // String
$age = 25;         // Integer
$active = true;    // Boolean
?>

Tip: Interviewers often ask if PHP is loosely typed. Yes, PHP is a loosely typed language.

3. PHP MySQL Interview Questions: Connecting & Querying a Database

How do you connect to a MySQL database and fetch data?

Example:

<?php
$conn = new mysqli("localhost", "root", "", "database");
if ($conn->connect_error) {
  die("Connection failed: " . $conn->connect_error);
}
$result = $conn->query("SELECT * FROM users");
while($row = $result->fetch_assoc()) {
  echo $row["name"] . "<br>";
}
?>

Quick Facts:

• You can use either mysqli or PDO
• Prepared statements are recommended for security and often asked in interviews

4. PHP Framework Interview Questions: Laravel

What is Laravel and why is it used?

Laravel is a robust PHP framework designed for building modern web applications. It follows the MVC pattern and simplifies tasks like routing, authentication, migrations, and ORM with Eloquent.

Example – Defining a Route in Laravel:

Route::get('/user', [UserController::class, 'index']);

Quick Facts:

• Be familiar with Artisan commands, middleware, and controller structures.
• Know commands like php artisan migrate and php artisan make:controller.

5. PHP WordPress Interview Questions

How do you build a custom theme in WordPress?

You create a theme by defining key files like style.css, functions.php, and index.php inside a theme folder.

Example – Registering a Menu in functions.php:

<?php
function register_my_menu() {
register_nav_menu('header-menu', __( 'Header Menu' ));
}
add_action('init', 'register_my_menu');
?>

Tip: Understanding the WordPress hook system (action/filter) and working with Custom Post Types (CPT) gives you an edge in WordPress interviews.

6. PHP Backend Interview Questions: Sessions, Cookies, and Authentication

What’s the difference between Session and Cookie?

• Session: Stored on the server
• Cookie: Stored in the browser

Example – Using Session in PHP:

<?php
session_start();
$_SESSION["user"] = "techcareer";
echo $_SESSION["user"];
?>

7. PHP Performance Optimization Interview Questions

How can you improve PHP application performance?

• Use OPcache for opcode caching
• Avoid loading unnecessary files (use autoloading)
• Optimize database queries
• Use CDN and caching systems (e.g., Redis, Memcached)
• Eliminate repetitive code

Example – Caching Query Results:

$cache = apcu_fetch('users');
if (!$cache) {
  $cache = $db->query("SELECT * FROM users")->fetchAll();
  apcu_store('users', $cache, 300);
}

8. PHP Error Handling Interview Questions

What’s the difference between Error and Exception?

• Error: System-level issues that typically can’t be caught
• Exception: Can be handled using try/catch blocks

Example – Handling Exceptions in PHP:

try {
  throw new Exception("An error occurred!");
} catch (Exception $e) {
  echo $e->getMessage();
}

9. PHP Design Pattern Interview Questions

What is the Singleton design pattern?

Singleton ensures that only one instance of a class is created and provides a global point of access.

Example – Singleton in PHP:

class DB {
  private static $instance;
  private function __construct() {}
  public static function getInstance() {
      if (!self::$instance) {
          self::$instance = new DB();
      }
      return self::$instance;
  }
}

10. Real-World Scenario Interview Question: E-Commerce Discount Logic

How would you implement a promotional discount system?

• Campaign rules are stored in the database
• Rules are triggered during checkout
• Eligible discounts are automatically calculated

Example – Discount Function:

function applyDiscount($amount) {
  if ($amount > 500) return $amount * 0.90;
  return $amount;
}

PHP, when structured properly, remains a powerful tool for developing modern, high-performance web applications. Interview questions typically cover PHP backend, Laravel, MySQL, WordPress, and performance optimization.

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