Show me the dates of those exhibitions
SELECT T1.date FROM exhibition_record AS T1 JOIN exhibition AS T2 ON T1.exhibition_id   =   T2.exhibition_id WHERE T1.attendance  >  500
dates of those exhibitions refers to SELECT date; exhibitions with more than 500 attendees refers to WHERE attendance > 500; joining exhibition_record with exhibition on exhibition_id refers to JOIN...ON T1.exhibition_id = T2.exhibition_id;