Question: Calculate the percentage of business which opened on Sunday from 9AM to 9PM based on the number of business opened on Sunday.
SQL: SELECT CAST(SUM(CASE WHEN T2.opening_time = '9AM' AND T2.closing_time = '9PM' THEN 1 ELSE 0 END) AS REAL) * 100 / COUNT(T1.day_id) FROM Days AS T1 INNER JOIN Business_Hours AS T2 ON T1.day_id = T2.day_id WHERE T1.day_of_week = 'Sunday'