CREATE TABLE table_name_90 (assists VARCHAR(255), opponent VARCHAR(255), team VARCHAR(255), competition VARCHAR(255), total_gs VARCHAR(255))
How many assists were in the k-league competition, which has more than 20 total Gs, the pohang steelers team, and chunnam dragons as the opponent?
    
SQL: SELECT assists FROM table_name_90 WHERE competition = "k-league" AND total_gs > 20 AND team = "pohang steelers" AND opponent = "chunnam dragons"