What best practices should be followed when handling user input and database queries in PHP scripts to prevent errors and vulnerabilities?

To prevent errors and vulnerabilities when handling user input and database queries in PHP scripts, it is essential to use prepared statements with parameterized queries to prevent SQL injection attacks. Additionally, input validation should be performed to ensure that only expected data is accepted, and output escaping should be used to prevent cross-site scripting attacks. 

// Example of using prepared statements with parameterized queries to prevent SQL injection attacks
$conn = new mysqli($servername, $username, $password, $dbname);

$stmt = $conn->prepare("SELECT * FROM users WHERE username = ?");
$stmt->bind_param("s", $username);

$username = $_POST['username'];
$stmt->execute();

$result = $stmt->get_result();
while ($row = $result->fetch_assoc()) {
    // Process the query result
}

$stmt->close();
$conn->close();

Keywords

SQL injection prepared statements input validation cross-site scripting PDO.

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