Hi, I was wondering how many users do not have tweets?
select count ( * ) from user_profiles where uid not in ( select uid from tweets )
Great, what is the average number of followers for everyone in the data set?
select avg ( followers ) from user_profiles
Okay, and what about the average followers for those who do have tweets?
select avg ( followers ) from user_profiles where uid in ( select uid from tweets )
And what was the average followers for those who do not have any tweets?
select avg ( followers ) from user_profiles where uid not in ( select uid from tweets )