SELECT count(DISTINCT winner_name) FROM matches WHERE tourney_name  =  'WTA Championships' AND winner_hand  =  'L'
Find the number of left handed winners who participated in the WTA Championships.
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 = value and winner_hand = value
Find the number of left handed winners who participated in the WTA Championships .