WordPress developers launched WordPress.Com’s debug bar for Self Hosted WordPress Blogs . It adds a debug menu to WP admin bar that shows query, cache, and other helpful debugging information. Good for developers.
When WP_DEBUG is enabled it also tracks PHP Warnings and Notices to make them easier to find. When SAVEQUERIES is enabled the mysql queries are tracked and displayed. Install and activate Debug Bar then try it yourself you can also add a PHP/MySQL console with Debug Bar Console plugin.