MySQL

Quick Introduction

MySQL is a single PHP idea you'll use in almost every backend project.

In this lesson you learn only mysql — not five topics at once. By the end you can write a small working example and explain it in an interview.

We connect each lesson to our course projects: Login System, Blog CMS, REST API, Inventory, Employee Management, and E-Commerce Backend.

Business Problem

You're building the Inventory Management. After a user signs in, you need mysql working correctly before storing data or showing a dashboard.

Without understanding MySQL, the team ships bugs: wrong totals, broken sessions, or type errors that only appear in production. This lesson fixes that with one clear pattern you can copy into your project today.

Core Concept

• MySQL is one focused idea — learn it before mixing with other PHP topics.
• Use it in PHP 8.3+ with declare(strict_types=1); at the top of every file.
• Our course project (Inventory Management) uses mysql in real handlers.
• Run small scripts with php file.php after each change — don't just read.
• Interviewers ask for a one-minute explanation plus a tiny code sample.

Syntax

Core syntax for MySQL. Every keyword below appears in production PHP — Laravel and Symfony use the same primitives under the hood.

declare(strict_types=1);

Keywords: declare · strict_types · namespace

Step-by-Step Example

Run this script locally. Change one value, run again, and watch what changes.

<?php
declare(strict_types=1);

$mysqli = new mysqli('127.0.0.1', 'app', 'secret', 'shop');
if ($mysqli->connect_error) {
    throw new RuntimeException($mysqli->connect_error);
}
$mysqli->set_charset('utf8mb4');

$result = $mysqli->query("SELECT id, name FROM categories WHERE active = 1 ORDER BY sort_order LIMIT 10");
$rows = $result->fetch_all(MYSQLI_ASSOC);

$stmt = $mysqli->prepare('UPDATE categories SET sort_order = ? WHERE id = ?');
$id = 5; $order = 2;
$stmt->bind_param('ii', $order, $id);
$stmt->execute();

print_r($rows);

Line by line

1. — part of the mysql example; run the file to see the result.
2. declare(strict_types=1); — turns on strict type checking for this file.
3. $mysqli = new mysqli('127.0.0.1', 'app', 'secret', 'shop'); — part of the mysql example; run the file to see the result.
4. if ($mysqli->connect_error) { — part of the mysql example; run the file to see the result.
5. throw new RuntimeException($mysqli->connect_error); — part of the mysql example; run the file to see the result.

Authenticated

Real-World Example

In the Inventory Management, mysql appears in a single request handler — not spread across ten files. Keep the example small, test it with php, then paste the pattern into your project branch.

<?php
declare(strict_types=1);

// TODO: MySQL exercise for Inventory Management