How to Prepare for a PHP Interview: Checklist with Code Examples

PHP Interview: Don't Fear, Prepare

An interview for a PHP developer position is not an exam on tickets, but a dialogue. However, it's a dialogue where they expect not just "I know PHP," but an understanding of how the language works under the hood. Preparing for a PHP interview is not about cramming definitions, but about analyzing real-world cases.

In this article, we won't list a hundred questions. Instead, I'll show you a thinking template: how to answer questions, how to write code, and what to pay attention to so the interviewer says "wow." Let's go.

1. PHP Basics: What You Must Know

Let's start with the basics. Even if you're aiming for a Senior position, basic questions can come up. Here are the three pillars of a PHP interview:

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• Data types and type casting — how == vs === works, what strict_types is.
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• Superglobal arrays — $_GET, $_POST, $_SERVER, $_SESSION.
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• Working with arrays — array_map, array_filter, array_reduce.
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Example question: "What will this code output?"

<?php\n$a = '5';\n$b = 5;\nvar_dump($a == $b);  // bool(true) — loose comparison\nvar_dump($a === $b); // bool(false) — strict comparison\n?>

Remember: a junior PHP interview is often built around such pitfalls. Don't fall for them.

2. OOP in PHP: Not Just "Class and Object"

PHP questions in interviews always include OOP. But instead of listing the three pillars (encapsulation, inheritance, polymorphism), show how you use them.

Example: they might ask about interfaces and abstract classes. Don't say "an interface is a contract." Better to provide code:

<?php\ninterface PaymentGateway {\n    public function pay(float $amount): bool;\n}\n\nclass StripeGateway implements PaymentGateway {\n    public function pay(float $amount): bool {\n        // payment logic via Stripe\n        return true;\n    }\n}\n\nclass PayPalGateway implements PaymentGateway {\n    public function pay(float $amount): bool {\n        // payment logic via PayPal\n        return true;\n    }\n}\n\nfunction processOrder(PaymentGateway $gateway, float $total) {\n    if ($gateway->pay($total)) {\n        echo "Payment successful";\n    }\n}\n?>

Such an answer shows that you understand the Liskov Substitution Principle and know how to design flexible systems. That's an instant +100 karma in a PHP middle interview.

3. Working with Databases: SQL and PDO

No PHP interview is complete without MySQL questions. Remember: never use mysql_* functions — they were removed in PHP 7. Use PDO or mysqli.

A typical task: "Write a secure database query."

<?php\n$pdo = new PDO('mysql:host=localhost;dbname=test', 'user', 'pass');\n$stmt = $pdo->prepare('SELECT * FROM users WHERE email = :email');\n$stmt->execute(['email' => $email]);\n$user = $stmt->fetch(PDO::FETCH_ASSOC);\n?>

Why is this important? Because SQL injections are a classic junior mistake. Show that you know about prepared statements.

Another common question is JOINs. Be ready to explain the difference between INNER, LEFT, RIGHT, and FULL JOIN. And be sure to give an example of when to use each.

4. Typical PHP Interview Tasks

PHP tasks are not just theory. You might be given a live coding exercise. Here are three types of tasks that often come up:

4.1. Array Task

"Write a function that groups an array of objects by a ke