Show the theme for exhibitions with records of an attendance above 500
SELECT T2.theme FROM exhibition_record AS T1 JOIN exhibition AS T2 ON T1.exhibition_id   =   T2.exhibition_id WHERE T1.attendance  >  500
attendance above 500 refers to attendance > 500; theme for exhibitions refers to selecting the theme column from the exhibitions table; linking exhibition records to specific exhibitions refers to JOIN operation on exhibition_record and exhibition tables based on a common exhibition_id.