Understanding How Parameterized Queries Work

Parameterized queries fundamentally change how databases process SQL statements. Instead of constructing complete SQL strings, applications send query templates with placeholders to the database. The database compiles this template once, creating an execution plan that treats placeholders as data values, not executable code. When actual values are provided, they're inserted into pre-defined data slots, preventing any possibility of SQL injection.

// PHP PDO implementation showing the process
$pdo = new PDO('mysql:host=localhost;dbname=test', $user, $pass);

// Step 1: Prepare the statement template
$stmt = $pdo->prepare('SELECT * FROM users WHERE age > :age AND city = :city');

// Step 2: Bind parameters (data never touches SQL structure)
$stmt->bindParam(':age', $age, PDO::PARAM_INT);
$stmt->bindParam(':city', $city, PDO::PARAM_STR);

// Step 3: Execute with actual values
$age = 25;
$city = "New York'; DROP TABLE users; --";  // Malicious input rendered harmless
$stmt->execute();

// The database sees this as searching for city literally named "New York'; DROP TABLE users; --"