Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE university ( school_id number, school text, location text, founded number, affiliation text, enrollment number, nickname text, primary_conference text )
TABLE: CREATE TABLE basketball_match ( team_id number, school_id number, team_name text, acc_regular_season text, acc_percent text, acc_home text, acc_road text, all_games text, all_games_percent number, all_home text, all_road text, all_neutral text )

### Question ###
Find the number of universities that have over a 20000 enrollment size for each affiliation type.

### Accurate SQL ###

SELECT COUNT(*), affiliation FROM university WHERE enrollment > 20000 GROUP BY affiliation