How to Pass a PHP Interview: Top Questions from A to Z

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How to Pass a PHP Interview: Top Questions from A to Z

An interview for a PHP developer position is not just a test of syntax knowledge. Employers want to see how you think, how you solve problems, and how deeply you understand the language ecosystem. To help you prepare, we have gathered top PHP questions from A to Z, broken down into key topics: from OOP basics to working with databases and security.

This article is your checklist for successfully passing the interview. Study it, practice with the code examples, and you will feel confident.

1. PHP Basics and OOP (Object-Oriented Programming)

Let's start with the fundamentals. Without understanding OOP in modern PHP, there's nothing to do. Interviewers often ask questions that test your understanding of the principles.

Question: What are encapsulation, inheritance, and polymorphism?

These are the "three pillars" of OOP. Being able to explain them with an example is a mandatory skill.

Encapsulation — hiding the internal implementation of an object. Data access is done through public methods (getters/setters).
Inheritance — the ability to create a new class based on an existing (parent) class.
Polymorphism — the ability of objects of different classes to handle the same method in their own way.

<?php// Example of encapsulationclass User {    private string $name;

    public function setName(string $name): void {        $this->name = htmlspecialchars($name); // Protection against XSS    }

    public function getName(): string {        return $this->name;    }}

// Example of inheritance and polymorphismabstract class Animal {    abstract public function makeSound(): string;}

class Dog extends Animal {    public function makeSound(): string {        return "Woof!";    }}

class Cat extends Animal {    public function makeSound(): string {        return "Meow!";    }}

$animals = [new Dog(), new Cat()];foreach ($animals as $animal) {    echo $animal->makeSound() . " "; // Outputs: Woof! Meow!}?>

Question: What is the difference between an interface and an abstract class?

This is a classic. An interface defines a contract (only method signatures), while an abstract class can contain default implementations and properties.

2. Working with Databases and SQL

PHP rarely works in isolation from databases. Questions about MySQL and PDO are a mandatory part of any interview.

Question: Why should you use PDO instead of mysqli?

PDO (PHP Data Objects) is an abstraction that allows you to easily switch between different DBMS (MySQL, PostgreSQL, SQLite) without rewriting code. Additionally, PDO supports named placeholders, which makes the code cleaner.

<?php// Example of a secure query with PDO$dsn = 'mysql:host=localhost;dbname=testdb;charset=utf8mb4';$pdo = new PDO($dsn, 'user', 'password');

$sql = "SELECT * FROM users WHERE email = :email";$stmt = $pdo->prepare($sql);$stmt->execute([':email' => 'test@example.com']);$user = $stmt->fetch(PDO::FETCH_ASSOC);?>

Question: How do you protect against SQL injections?

The main answer: never insert user data directly into an SQL query. Use prepared statements with placeholders. This ensures that the data will be escaped automatically.