MySQL & PDO

<?php
// PDO connection
$dsn = "mysql:host=localhost;dbname=myapp;charset=utf8mb4";
$pdo = new PDO($dsn, 'root', 'password', [
    PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
    PDO::ATTR_EMULATE_PREPARES   => false,
]);

// SELECT — always use prepared statements
$stmt = $pdo->prepare("SELECT * FROM users WHERE email = :email");
$stmt->execute(['email' => $email]);
$user  = $stmt->fetch();
$users = $stmt->fetchAll();

// INSERT
$stmt = $pdo->prepare("INSERT INTO users (name, email) VALUES (:name, :email)");
$stmt->execute(['name' => $name, 'email' => $email]);
$id = $pdo->lastInsertId();

// Transaction
$pdo->beginTransaction();
try {
    $pdo->prepare("UPDATE accounts SET balance=balance-? WHERE id=?")
        ->execute([100, $from]);
    $pdo->commit();
} catch (Exception $e) {
    $pdo->rollBack();
}