5 Fatal Mistakes When Learning PHP: A Checklist for Beginners

Introduction: Why Some Give Up on PHP While Others Make Money with It

You've decided to learn PHP. Great choice! This language powers 78% of all websites on the internet — from simple blogs to giants like Facebook (well, almost). But there's one problem: many beginners make the same mistakes that turn learning into a nightmare.

Why does this happen? PHP is a tricky language. It forgives stupid mistakes, but it does not forgive ignorance of basic principles. You write code, it works, the site loads — and you think everything is great. But a month later, you can't make sense of your own 500-line mess, and your site gets hacked in 5 minutes.

In this article, I'll break down the 5 most common mistakes when learning PHP that beginners make. I'll show real code examples, explain why doing it that way is bad, and give concrete solutions. If you recognize yourself in at least one point — don't worry, it's normal. Just fix it.

Mistake #1: Mixing PHP and HTML in One File Without Structure

This is a classic. A beginner writes something like:

<?php\n$username = "Ivan";\necho "<html><body><h1>Hello, " . $username . "!</h1>";\n?>\n<p>This is text after PHP</p>\n<?php\necho "</body></html>";\n?>

It seems to work. But try adding a loop, a condition, ten pages — and you'll drown in a mess of tags and echo. Such code is impossible to read, maintain, and debug.

Why is this bad?

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• It violates the separation of concerns principle (MVC).
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• With the slightest design change, you rewrite half the logic.
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• Code editors go crazy with mixed tags.
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How to do it right?

Use templating. Even without frameworks, you can separate logic from presentation:

<?php\n// logic.php\n$data = ['name' => 'Ivan', 'age' => 25];\ninclude 'template.php';\n?>\n\n<!-- template.php -->\n<!DOCTYPE html>\n<html>\n<body>\n    <h1><?= htmlspecialchars($data['name']) ?></h1>\n    <p>Age: <?= $data['age'] ?> years</p>\n</body>\n</html>

Notice: I used the short tag <?= and the htmlspecialchars() function — this is already protection against XSS. Mistakes when learning PHP are often related precisely to ignoring security.

Mistake #2: Ignoring SQL Injections (The Most Dangerous)

In 2025, writing code like this is a crime:

$id = $_GET['id'];\n$query = "SELECT * FROM users WHERE id = $id";\n$result = mysqli_query($conn, $query);

If you pass ?id=1 OR 1=1 in the URL, you'll get all users. If you pass ?id=1; DROP TABLE users — goodbye database. This is an SQL injection, and it's the first thing hackers check.

How to fix it?

Use prepared statements. Here's how it's done in modern PHP with PDO:

$pdo = new PDO('mysql:host=localhost;dbname=test', 'root', '');\n$stmt = $pdo->prepare('SELECT * FROM users WHERE id = :id');\n$stmt->execute(['id' => $_GET['id']]);\n$user = $stmt->fetch();

The database itself escapes the value. An injection becomes impossible. Remember: never insert user data directly into an SQL query. This is one of the main mistakes when learning PHP that can cost you your site.

Mistake #3: Using Outdated Functions and Styles

The internet is full of tutorials from 2010 that teach:

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• mysql_connect() — removed in PHP 7.0.
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• ereg() instead of preg_match().
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• split() instead of explode().
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• Closing the ?> tag at the end of a pure PHP file.
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Why is this bad? Because