Sql Query Needed
 

I have a forum where one of the users didnt port from phpbb and his posts are set to Guest

All of the guys posts have his username typed in so i need a query to search for all his posts with X text and update each post to his new userID

I can do the posts one by one with :

UPDATE post SET userid='XXX' WHERE postid='XXX'

But he has hundreds of posts - all with the common denominator of having X text string in each post so it would take HOURS if i did it manually

Thanks