Question: What are the categories of businesses that have opening time on Sunday?
SQL: SELECT DISTINCT T1.category_name FROM Categories AS T1 INNER JOIN Business_Categories AS T2 ON T1.category_id = T2.category_id INNER JOIN Business_Hours AS T3 ON T2.business_id = T3.business_id INNER JOIN Days AS T4 ON T3.day_id = T4.day_id WHERE T4.day_of_week = 'Sunday' AND T3.opening_time <> ''