-- Database schema
| follows : f1 [ INT ] primary_key follows.f1 = user_profiles.uid , f2 [ INT ] follows.f2 = user_profiles.uid | tweets : id [ INT ] primary_key , uid [ INT ] tweets.uid = user_profiles.uid , text [ TEXT ] , createdate [ TEXT ] | user_profiles : uid [ INT ] primary_key , name [ TEXT ] , email [ TEXT ] , partitionid [ INT ] , followers [ INT ] |
-- -- Find the number of users who posted some tweets.

SELECT count(DISTINCT UID) FROM tweets;