Database: wta_1 (difficulty: simple)
Question: What are the first names and country codes for players who won both the Kaohsiung and the Australian Open?
SQL: SELECT T1.country_code ,  T1.first_name FROM players AS T1 JOIN matches AS T2 ON T1.player_id  =  T2.winner_id WHERE T2.tourney_name  =  'Kaohsiung' INTERSECT SELECT T1.country_code ,  T1.first_name FROM players AS T1 JOIN matches AS T2 ON T1.player_id  =  T2.winner_id WHERE T2.tourney_name  =  'Australian Open'