If you're preparing for a web development interview, especially for a backend role, chances are high that you'll encounter several PHP-related questions. PHP remains one of the most widely used server-side scripting languages and continues to play a vital role in building dynamic web applications.

To help you crack your next interview, we've compiled a list of the most frequently asked PHP interview questions with answers. These are curated based on real interview experiences and are designed to test both basic and advanced knowledge of PHP.

1. What is PHP?
   Answer:
   PHP stands for Hypertext Preprocessor. It is a widely-used, open-source server-side scripting language that is especially suited for web development. It can be embedded into HTML and is commonly used to create dynamic page content, manage databases, session tracking, and even build entire eCommerce sites.

2. What are the different types of variables in PHP?
   Answer:
   PHP supports several types of variables, including:

String – A sequence of characters.

Integer – Whole numbers.

Float (Double) – Numbers with decimal points.

Boolean – TRUE or FALSE.

Array – A collection of values.

Object – An instance of a class.

NULL – A variable with no value.

1. Explain the difference between == and === in PHP. Answer:

== checks only for equality of value, not data type.

=== checks for both value and data type.

Example:

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5 == "5" // true

5 === "5" // false

1. What is the difference between include and require? Answer:

include: Emits a warning if the file is not found but continues script execution.

require: Emits a fatal error and stops the script if the file is missing.

Use require when the file is essential for the application to run.

1. What are sessions and how are they different from cookies? Answer: Sessions store data on the server, while cookies store data in the user's browser.

Sessions are more secure and ideal for storing sensitive information like user login details.

Cookies are best for non-sensitive data and have size limitations.

1. How do you connect to a MySQL database using PHP? Answer: You can use the mysqli_connect() function:

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$conn = mysqli_connect("localhost", "username", "password", "database");
if (!$conn) {
die("Connection failed: " . mysqli_connect_error());
}

1. What is the difference between GET and POST methods? Answer:

GET: Appends data to the URL and has length limitations. Suitable for non-sensitive data.

POST: Sends data via HTTP headers and is more secure. Ideal for form submissions like passwords.

1. What are some common PHP error types? Answer:

Parse Error: Syntax mistake.

Fatal Error: When PHP cannot perform a critical operation (e.g., undefined function).

Warning: Non-critical error; script continues.

Notice: Minor error, like using an undefined variable.

1. What is PDO in PHP?
   Answer:
   PDO (PHP Data Objects) is a database access layer providing a uniform method of access to multiple databases. It offers a more secure and flexible way to interact with databases compared to mysqli.

2. What is an associative array in PHP?
   Answer:
   An associative array uses named keys that you assign to them, rather than numeric keys.

Example:

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$person = array("name"=>"John", "age"=>25);

1. How does PHP handle form submission? Answer: PHP can collect form data sent using GET or POST methods using $_GET and $_POST superglobals.

Example:

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$name = $_POST['name'];
echo "Hello, $name!";

1. What is the use of isset() and empty() in PHP? Answer:

isset(): Checks if a variable is set and not NULL.

empty(): Checks if a variable is empty (i.e., "", 0, NULL, FALSE, etc.)

1. What is the use of explode() and implode() functions? Answer:

explode(): Splits a string into an array.

implode(): Joins array elements into a string.

Example:

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$arr = explode(",", "apple,banana,mango");
$str = implode("-", $arr);

1. Can PHP support object-oriented programming (OOP)? Answer: Yes, PHP supports OOP principles such as:

Classes and Objects

Inheritance

Encapsulation

Polymorphism

Interfaces

OOP in PHP enhances code reusability and organization.

1. How can you prevent SQL injection in PHP? Answer: By using prepared statements with mysqli or PDO, you can safely pass user input to SQL queries without directly concatenating strings.

Example using mysqli:

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$stmt = $conn->prepare("SELECT * FROM users WHERE email = ?");
$stmt->bind_param("s", $email);
$stmt->execute();
Final Thoughts
Whether you're a fresher or an experienced developer, reviewing the most frequently asked PHP interview questions with answers can be a real game-changer for your job preparation. These questions cover both foundational concepts and practical skills expected in real-world scenarios.

Remember, an effective PHP interview question and answer session isn't just about getting the right answers—it's about demonstrating your understanding and problem-solving approach. Practice these well, and you'll walk into your next PHP interview with confidence!