Context: CREATE TABLE matches (winner_id VARCHAR, tourney_name VARCHAR); CREATE TABLE players (country_code VARCHAR, first_name VARCHAR, player_id VARCHAR)
Question: What are the country code and first name of the players who won in both tourney WTA Championships and Australian Open?
Answer: 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 = 'WTA Championships' 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'