-- Database schema
| museum : Museum_ID [ INT ] primary_key , Name [ TEXT ] , Num_of_Staff [ INT ] , Open_Year [ TEXT ] | visitor : ID [ INT ] primary_key , Name [ TEXT ] , Level_of_membership [ INT ] , Age [ INT ] | visit : Museum_ID [ INT ] primary_key visit.Museum_ID = museum.Museum_ID , visitor_ID [ TEXT ] visit.visitor_ID = visitor.ID , Num_of_Ticket [ INT ] , Total_spent [ INT ] |
-- -- Find the number of visitors who did not visit any museum opened after 2010.

SELECT count(*) FROM visitor WHERE id NOT IN (SELECT t2.visitor_id FROM museum AS t1 JOIN visit AS t2 ON t1.Museum_ID  =  t2.Museum_ID WHERE t1.open_year  >  2010);