I have (a.o.) two MySQL tables with (a.o.) the following columns:

tweets:
-------------------------------------
id text        from_user_id from_user
-------------------------------------
1  Cool tweet! 13295354     tradeny
2  Tweeeeeeeet 43232544     bolleke
3  Yet another 13295354     tradeny
4  Something.. 53546443     janusz4

users:
-------------------------------------
id from_user num_tweets from_user_id
-------------------------------------
1  tradeny   2235
2  bolleke   432
3  janusz4   5354

I now want to normalize the tweets table, replacing tweets.from_user with an integer that matches users.id. Secondly, I want to fill in the corresponding users.from_user_id, Finally, I want to delete tweets.from_user_id so that the end result would look like:

tweets:
------------------------
id text        from_user
------------------------
1  Cool tweet!     1
2  Tweeeeeeeet     2
3  Yet another     1
4  Something..     3

users:
-------------------------------------
id from_user num_tweets from_user_id
-------------------------------------
1  tradeny   2235       13295354
2  bolleke   432        43232544
3  janusz4   5354       53546443

My question is whether one could help me form the proper queries for this. I have only come so far:

UPDATE tweets SET from_user =
  (SELECT id FROM users WHERE from_user = tweets.from_user)
WHERE...

UPDATE users SET from_user_id =
  (SELECT from_user_id FROM tweets WHERE from_user = tweets.from_user)
WHERE...

ALTER TABLE tweets DROP from_user_id

Any help would be greatly appreciated :-)