What is the average winning margin of all the matches SC Ganguly has played in?
SC Ganguly refers to Player_Name = 'SC Ganguly'; the average winning margin = divide(sum(Win_Margin), count(Match_Id)) where Player_Name = 'SC Ganguly'
SELECT CAST(SUM(T3.Win_Margin) AS REAL) / COUNT(*) FROM Player AS T1 INNER JOIN Player_Match AS T2 ON T1.Player_Id = T2.Player_Id INNER JOIN Match AS T3 ON T2.Match_Id = T3.Match_Id WHERE T1.Player_Name = 'SC Ganguly'