What are common pitfalls to avoid when concatenating SQL queries in PHP using the concatenation assignment operator?

When concatenating SQL queries in PHP using the concatenation assignment operator (.=), it is important to ensure that each query segment is properly sanitized to prevent SQL injection attacks. Common pitfalls to avoid include not properly escaping special characters, not using prepared statements, and not validating user input. 

// Example of concatenating SQL queries safely using prepared statements

// Initialize the SQL query as an empty string
$sql = "";

// Concatenate the query segments safely
$userInput = $_POST['user_input'];
$userInput = mysqli_real_escape_string($connection, $userInput); // Sanitize user input
$sql .= "SELECT * FROM users WHERE username = ?";
$sql .= " AND email = ?";
$stmt = $connection->prepare($sql);
$stmt->bind_param("ss", $userInput, $userInput);
$stmt->execute();

Keywords

SQL injection concatenation assignment operator prepared statements mysqli_real_escape_string security

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