The PHP project is working toward “softly” deprecating the mysql extension and its associated functions in favor of the newer (and more secure) mysqli and PDO extensions. They won’t be adding E_DEPRECATED errors for the extension in PHP 5.4, but will consider it in subsequent versions. Instead they will be focusing on education, marking it as deprecated in the documentation, adding new documents about the differences, as well as updating examples throughout to use the more modern functions.
The situation is certainly…interesting. There is a lot of code out there using the older database functions—to the point that I’m more surprised to see PDO or MySQLi in use—and nearly as many tutorials teaching questionable practices that enable injection attacks. It’s going to take quite a long time to move people toward the better extension, especially when you consider how long it took for web hosts to roll out PHP 5 when it’s backwards-compatibility issues were relatively minor.
Deprecating ext/mysql [news.php.net]