Calculate the percentage of left hand batting style players among all players.
left hand batting style players refers to Batting_hand = 'Left-hand bat'; percentage refers to DIVIDE(COUNT(Batting_hand = 'Left-hand bat'), COUNT(Player_Id)) * 100.0
SELECT CAST(SUM(CASE WHEN T2.Batting_hand = 'Left-hand bat' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.Player_Id) FROM Player AS T1 INNER JOIN Batting_Style AS T2 ON T1.Batting_hand = T2.Batting_Id