For SQL Server there is a commercial product called SQL
Compare which is awesome, I do not use MySQL anymore so I am a
little out of touch on that front, but there may be a similar
product.
What suggest you do is restore your production database in
your dev environment and then write all the alter scripts you need
and test them on that copy and then test your dev application
against it. Then you can be confident that you can ally them to
live.
In future you should try and do code releases that include
database schema changes coupled with code releases, this makes life
much easier. As always I would suggest using svn (subversion) to
help with this as it is free and basically awesome.