For each perpetrator, show the ids and his or her country.
select country, perpetrator_id from perpetrator;
Also, show how many they have each injured.
select country, perpetrator_id, injured from perpetrator;
Which countries have perpetrators who have injured more than 50?
select country from perpetrator where injured > 50;
Which of these also have perpetrators who have injured fewer than 20?
select country from perpetrator where injured > 50 intersect select country from perpetrator where injured < 20;