How can using variables in SQL queries in PHP improve code readability and maintainability?

Using variables in SQL queries in PHP can improve code readability and maintainability by allowing you to easily update and modify the query without having to search through the entire codebase. It also helps prevent SQL injection attacks by properly escaping user input. Additionally, using variables can make the code more organized and easier to understand for other developers.

// Example of using variables in SQL queries in PHP
$userId = 123;
$sql = "SELECT * FROM users WHERE id = $userId";
$result = mysqli_query($conn, $sql);