What is the potential issue with the mysql_num_rows() function in the PHP code provided?

The potential issue with the mysql_num_rows() function is that it is deprecated in newer versions of PHP and has been removed in PHP 7.0. It is recommended to use the mysqli_num_rows() function instead, which is the improved version for MySQLi extension. To fix the issue, you should replace mysql_num_rows() with mysqli_num_rows() in the code.

// Original code with mysql_num_rows() function
$result = mysql_query("SELECT * FROM users");
$num_rows = mysql_num_rows($result);

// Updated code with mysqli_num_rows() function
$result = mysqli_query($conn, "SELECT * FROM users");
$num_rows = mysqli_num_rows($result);