Among the players born in 1977, what is the percentage of the players with a role as a captain?
born in 1977 refers to DOB LIKE '1977%'; a role as a captain refers to Role_Desc = 'Captain'; percentage = divide(count(Role_Id where Role_Desc = 'Captain'), count(Role_Id)) * 100% where DOB LIKE '1977%'
SELECT CAST(SUM(CASE WHEN T1.Role_Desc = 'Captain' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.Role_Id) FROM Rolee AS T1 INNER JOIN Player_Match AS T2 ON T2.Role_Id = T1.Role_Id INNER JOIN Player AS T3 ON T3.Player_Id = T2.Player_Id WHERE T3.DOB LIKE '1977%'