I'm testing out this comment script and the author did not include any indexes. I was able to go through the script and index everything - except the LEFT JOIN.
SELECT DISTINCT pac2_titles.title AS page_title, pac2_notifications.* FROM pac2_notifications LEFT JOIN pac2_titles ON pac2_titles.uri = pac2_notifications.what WHERE `what` = '/demo.php' AND `email` != 'firstname.lastname@example.org'
Any ideas how to properly index this?