I just ugpraded to WordPress 2.6.1, following my usual procedure (backup, download, extract over existing blog). I got some errors when I clicked to update the database:
WordPress database error: [Duplicate key name 'comment_approved']
ALTER TABLE nikolaidis_wp_comments ADD KEY comment_approved (comment_approved)
WordPress database error: [Duplicate key name 'type_status_date']
ALTER TABLE nikolaidis_wp_posts ADD KEY type_status_date (post_type,post_status,post_date,ID)
Your WordPress database has been successfully upgraded!
Given the last line, I’m inclined to think that these database upgrades may have been done in the 2.6 upgrade I did a while back.
At least, that’s my hope…