CRUD PHP and MySQL and API and Important Fundamentals

How to create a CRUD (Create, Read, Update, Delete) in PHP with MySQL.

This example uses the MySQLi extension to perform database operations.

Step 1: Creating the Database and Table

Run the following SQL script to create the database and a table called users:

CREATE DATABASE crud_example;
USE crud_example;

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE
);

---

Step 2: Connection to the Database

Create a config.php file to manage the database connection:

<?php $servername = "localhost";
$username = "root";
$password = "";
$dbname = "crud_example";

// Conexão com o banco
$conn = new mysqli($servername, $username, $password, $dbname);

// Verifica conexão
if ($conn->connect_error) {
    die("Falha na conexão: " . $conn->connect_error);
}
?>

---

Step 3: Home Page

Create an index.php file to list users and add creation, editing and deletion functionality:

<?php include 'config.php';

// Leitura dos dados
$sql = "SELECT * FROM users";
$result = $conn->query($sql);
?>




    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CRUD em PHP</title>


    <h1 id="Lista-de-Usuários">Lista de Usuários</h1>
    <a href="create.php">Adicionar Novo Usuário</a>
    

fetch_assoc()) { ?>

ID	Nome	Email	Ações
= $row['id'] ?>	= $row['name'] ?>	= $row['email'] ?>	Editar Excluir

---

Step 4: Create User

Create a create.php file to add a new user:

<?php include 'config.php';

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    $name = $_POST['name'];
    $email = $_POST['email'];

    $sql = "INSERT INTO users (name, email) VALUES ('$name', '$email')";
    if ($conn->query($sql) === TRUE) {
        header("Location: index.php");
        exit;
    } else {
        echo "Erro: " . $conn->error;
    }
}
?>




    <meta charset="UTF-8">
    <title>Criar Usuário</title>


    <h1 id="Adicionar-Novo-Usuário">Adicionar Novo Usuário</h1>
    

Nome:

---

Passo 5: Editar Usuário

Crie um arquivo edit.php para editar um usuário existente:

<?php include 'config.php';

$id = $_GET['id'];
$sql = "SELECT * FROM users WHERE id = $id";
$result = $conn->query($sql);
$user = $result->fetch_assoc();

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    $name = $_POST['name'];
    $email = $_POST['email'];

    $sql = "UPDATE users SET name='$name', email='$email' WHERE>




<hr>

<h3>
  
  
  Passo 6: Excluir Usuário
</h3>

<p>Crie um arquivo delete.php para excluir um usuário:<br>
</p>

<pre class="brush:php;toolbar:false"><?php include 'config.php';

$id = $_GET['id'];
$sql = "DELETE FROM users WHERE>




<hr>

<h3>
  
  
  Como Rodar o Projeto
</h3>

<ol>
<li>Configure o servidor local (como XAMPP ou LAMP).</li>
<li>Coloque todos os arquivos em uma pasta dentro do diretório público (htdocs ou equivalente).</li>
<li>Acesse http://localhost/sua_pasta/index.php no navegador.</li>
</ol>

<p>Esse é um CRUD básico e pode ser melhorado com validações, segurança (como SQL Injection), e estruturação MVC.</p>


<hr>

<h2>
  
  
  CRUD usando PHP e MySQL, estruturado de forma <strong>orientada a objetos (OOP)</strong>
</h2>

<p>A abordagem inclui uma classe para gerenciar as operações do banco de dados e separação lógica.</p>


<hr>

<h3>
  
  
  Passo 1: Configuração da Conexão com o Banco
</h3>

<p>Crie um arquivo Database.php para encapsular a conexão com o banco:<br>
</p>

<pre class="brush:php;toolbar:false"><?php class Database {
    private $host = "localhost";
    private $user = "root";
    private $pass = "";
    private $dbname = "crud_example";
    public $conn;

    public function __construct() {
        $this->conn = new mysqli($this->host, $this->user, $this->pass, $this->dbname);

        if ($this->conn->connect_error) {
            die("Erro na conexão: " . $this->conn->connect_error);
        }
    }
}
?>

---

Step 2: Class for Bank Operations

Create a User.php file to manage CRUD operations:

<?php include 'Database.php';

class User {
    private $db;

    public function __construct() {
        $this->db = (new Database())->conn;
    }

    // Create
    public function create($name, $email) {
        $stmt = $this->db->prepare("INSERT INTO users (name, email) VALUES (?, ?)");
        $stmt->bind_param("ss", $name, $email);
        return $stmt->execute();
    }

    // Read
    public function getAll() {
        $result = $this->db->query("SELECT * FROM users");
        return $result->fetch_all(MYSQLI_ASSOC);
    }

    public function getById($id) {
        $stmt = $this->db->prepare("SELECT * FROM users WHERE id = ?");
        $stmt->bind_param("i", $id);
        $stmt->execute();
        return $stmt->get_result()->fetch_assoc();
    }

    // Update
    public function update($id, $name, $email) {
        $stmt = $this->db->prepare("UPDATE users SET name = ?, email = ? WHERE id = ?");
        $stmt->bind_param("ssi", $name, $email, $id);
        return $stmt->execute();
    }

    // Delete
    public function delete($id) {
        $stmt = $this->db->prepare("DELETE FROM users WHERE id = ?");
        $stmt->bind_param("i", $id);
        return $stmt->execute();
    }
}
?>

---

Step 3: Home Page

Create an index.php file to display the list of users and manage navigation:

<?php include 'User.php';

$user = new User();
$users = $user->getAll();
?>




    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CRUD OOP PHP</title>


    <h1 id="Lista-de-Usuários">Lista de Usuários</h1>
    <a href="create.php">Adicionar Novo Usuário</a>
    

ID	Nome	Email	Ações
= $u['id'] ?>	= $u['name'] ?>	= $u['email'] ?>	Editar Excluir

---

Step 4: Create User

Create a create.php file to add new users:

<?php include 'User.php';

$user = new User();

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    $name = $_POST['name'];
    $email = $_POST['email'];

    if ($user->create($name, $email)) {
        header("Location: index.php");
        exit;
    } else {
        echo "Erro ao criar usuário.";
    }
}
?>




    <meta charset="UTF-8">
    <title>Criar Usuário</title>


    <h1 id="Adicionar-Novo-Usuário">Adicionar Novo Usuário</h1>
    

Nome:

---

Passo 5: Editar Usuário

Crie um arquivo edit.php para atualizar os dados do usuário:

<?php include 'User.php';

$user = new User();
$id = $_GET['id'];
$data = $user->getById($id);

if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    $name = $_POST['name'];
    $email = $_POST['email'];

    if ($user->update($id, $name, $email)) {
        header("Location: index.php");
        exit;
    } else {
        echo "Erro ao atualizar usuário.";
    }
}
?>




    <meta charset="UTF-8">
    <title>Editar Usuário</title>


    <h1 id="Editar-Usuário">Editar Usuário</h1>
    

Nome:

---

Passo 6: Excluir Usuário

Crie um arquivo delete.php para deletar um usuário:

<?php include 'User.php';

$user = new User();
$id = $_GET['id'];

if ($user->delete($id)) {
    header("Location: index.php");
    exit;
} else {
    echo "Erro ao excluir usuário.";
}
?>

---

How to Run the Project

1. Set up local server (like XAMPP or LAMP).
2. Create the database using SQL at first.
3. Place all files in a folder in the public directory.
4. Go to http://localhost/your_pasta/index.php in your browser.

This example is a basis for an object-oriented CRUD and can be improved with good practices, such as input validation, more robust error handling, and the use of namespaces.

Here is an example of how to create two APIs in PHP: one backend API to be consumed and another as client to consume the first API.

---

Creating the API to be consumed (Backend)

Step 1: Database Structure

Create a users table in the database:

CREATE DATABASE api_example;
USE api_example;

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE
);

Step 2: API Backend

Create a file called api.php to make the endpoints available.

<?php header("Content-Type: application/json");

include 'Database.php';

class UserAPI {
    private $db;

    public function __construct() {
        $this->db = (new Database())->conn;
    }

    public function handleRequest() {
        $method = $_SERVER['REQUEST_METHOD'];
        $endpoint = $_GET['endpoint'] ?? '';

        switch ($endpoint) {
            case 'users':
                if ($method === 'GET') {
                    $this->getUsers();
                } elseif ($method === 'POST') {
                    $this->createUser();
                } else {
                    $this->response(405, "Method Not Allowed");
                }
                break;

            default:
                $this->response(404, "Endpoint Not Found");
        }
    }

    private function getUsers() {
        $result = $this->db->query("SELECT * FROM users");
        $users = $result->fetch_all(MYSQLI_ASSOC);
        $this->response(200, $users);
    }

    private function createUser() {
        $input = json_decode(file_get_contents("php://input"), true);

        if (empty($input['name']) || empty($input['email'])) {
            $this->response(400, "Missing required fields: name or email");
            return;
        }

        $stmt = $this->db->prepare("INSERT INTO users (name, email) VALUES (?, ?)");
        $stmt->bind_param("ss", $input['name'], $input['email']);

        if ($stmt->execute()) {
            $this->response(201, "User created successfully");
        } else {
            $this->response(500, "Internal Server Error");
        }
    }

    private function response($status, $data) {
        http_response_code($status);
        echo json_encode(["status" => $status, "data" => $data]);
    }
}

$api = new UserAPI();
$api->handleRequest();
?>

---

2. Creating the Client to Consume API

API Client

Create a file called client.php to consume the backend API.

CREATE DATABASE crud_example;
USE crud_example;

CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE
);

---

3. Testing the API

Step 1: Configure the local environment

1. Set up your local server (XAMPP, LAMP or similar).
2. Place the api.php and client.php files in the same public folder.

Step 2: Test

1. API Backend: Go to http://localhost/api.php?endpoint=users to check the API endpoint.
2. Client: Run the client.php file in the terminal or through the browser to test consumption.

---

This example is a functional basis. For production, it is recommended:

• Use authentication tokens (like JWT).
• Add data validation and sanitization.
• Improve error management and HTTP responses.

---

If you are preparing for a technical interview for a junior developer with PHP and MySQL, here are the main topics that are usually covered, plus some tips:

---

PHP Fundamentals

• Basic syntax: Knowledge about variables, arrays, strings, loops, functions and control structures.
• Built-in functions: Manipulation of strings (e.g., explode, implode, trim), arrays (array_merge, array_filter) and numbers (round, rand).
• Object Orientation (OOP): Classes, objects, inheritance, encapsulation, polymorphism and interfaces.
• Working with files: fopen, fwrite, file_get_contents.
• Error and exception handling: try-catch and how to handle errors in PHP.
• Superglobals: $_POST, $_GET, $_SESSION, $_COOKIE, and how to use them.

2. MySQL and PHP Integration

• Basic queries: SELECT, INSERT, UPDATE, DELETE, with and without clauses such as WHERE, ORDER BY and LIMIT.
• Joins: Know how to use INNER JOIN, LEFT JOIN, RIGHT JOIN.
• Relationships: Work with related tables (1:1, 1:N, N:N).
• CRUD with PDO or MySQLi: Knowledge in executing queries and protecting against SQL Injection using prepared queries.
• Indices: What they are and how they help performance.
• Transactions: Concept and use in MySQL (START TRANSACTION, COMMIT, ROLLBACK).

3. Data Structure and Logic

• Basic algorithms: Sorting (Bubble Sort, Quick Sort), search (binary, linear).
• Data structures: Arrays, stacks, queues, lists.
• Troubleshooting: Experience solving small logic problems, such as those found in technical challenges (e.g., HackerRank, Codewars).

4. Good Practices and Standards

• Clean Code: Use of descriptive variable and function names, well-indented code.
• DRY (Don't Repeat Yourself) and KISS (Keep It Simple, Stupid).
• Basic security: Prevention against SQL Injection, XSS and CSRF.

5. Web Development

• Basic HTML/CSS/JavaScript: Sufficient knowledge to work with backends that interact with frontends.
• Forms: Forms processing, server-side validation.
• RESTful APIs: How to create and consume APIs, HTTP methods (GET, POST, PUT, DELETE).
• Sessions and authentication: Using $_SESSION and basic login/logout management.

6. Tools and Environment

• Versioning with Git: Commit, branch, merge and how to create pull requests.
• PHP Composer: Understand how to use external dependencies.
• Local environment: Experience with WAMP, XAMPP or Docker.
• Debugging: Use of var_dump, print_r, or tools like Xdebug.

7. Basic Concepts of Software Engineering

• Architecture models: MVC (Model-View-Controller).
• Relational database: Normalization of tables, primary and foreign keys.
• Version control: Work with Git repositories and understand team workflow (e.g., Git Flow).

8. Behavioral Questions

Junior companies also evaluate soft skills. Prepare for questions like:

• Why did you choose PHP?
• How do you solve problems under pressure?
• Tell me about a project you have already developed.
• How do you deal with errors?

---

Tips to Stand Out

1. Design something practical before the interview: Example, a simple CRUD, a RESTful API, or a basic login system. This shows your proactivity.
2. Get to know the company: Understand what it does, its technologies and see if you can align your answers with your needs.
3. Be honest: It's normal not to know everything. Demonstrate a willingness to learn and how you resolve gaps in knowledge.

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