Database: network_2
Question: What are the names of the people who are older 40 but no friends under age 30?
SQL: select t1.name from person as t1 join personfriend as t2 on t1.name  =  t2.name where t2.friend in (select name from person where age  >  40) except select t1.name from person as t1 join personfriend as t2 on t1.name  =  t2.name where t2.friend in (select name from person where age  <  30)