CREATE TABLE exhibition (theme VARCHAR(255), exhibition_id VARCHAR(255)); CREATE TABLE exhibition_record (exhibition_id VARCHAR(255), attendance INTEGER)
Show the theme for exhibitions with both records of an attendance below 100 and above 500.
    
SQL: SELECT T2.theme FROM exhibition_record AS T1 JOIN exhibition AS T2 ON T1.exhibition_id = T2.exhibition_id WHERE T1.attendance < 100 INTERSECT SELECT T2.theme FROM exhibition_record AS T1 JOIN exhibition AS T2 ON T1.exhibition_id = T2.exhibition_id WHERE T1.attendance > 500