What are the common mistakes to avoid when using multiple queries in PHP for data retrieval?

One common mistake to avoid when using multiple queries in PHP for data retrieval is not properly sanitizing user input, which can lead to SQL injection attacks. To prevent this, always use prepared statements with parameterized queries to securely pass user input to the database. 

// Connect to the database
$pdo = new PDO('mysql:host=localhost;dbname=mydatabase', 'username', 'password');

// Prepare a statement with a parameterized query
$stmt = $pdo->prepare('SELECT * FROM users WHERE username = :username');

// Bind the parameter and execute the query
$stmt->bindParam(':username', $_POST['username']);
$stmt->execute();

// Fetch the results
$results = $stmt->fetchAll(PDO::FETCH_ASSOC);

// Loop through the results and do something with them
foreach ($results as $row) {
    echo $row['username'] . '<br>';
}

Keywords

SQL injection PDO prepared statements database connection error handling

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