How many different winners both participated in the WTA Championships and were left handed?
SELECT count(DISTINCT winner_name) FROM matches WHERE tourney_name  =  'WTA Championships' AND winner_hand  =  'L'
SELECT count(DISTINCT winner_name) FROM matches WHERE tourney_name  =  'WTA Championships' AND winner_hand  =  'L'
[{'count(DISTINCT winner_name)': 2}]