What are the common issues faced by users when transitioning from PHP 4 to PHP 5 on a server?

One common issue faced by users when transitioning from PHP 4 to PHP 5 is the deprecated use of the "mysql_" functions. To solve this, users should switch to using the improved "mysqli_" functions or PDO for database interactions.

// Deprecated MySQL connection in PHP 4
$connection = mysql_connect($host, $username, $password);

// Updated MySQLi connection in PHP 5
$connection = mysqli_connect($host, $username, $password, $database);