Table schema:
CREATE TABLE dorm (dorm_name VARCHAR, dormid VARCHAR); CREATE TABLE lives_in (stuid VARCHAR, dormid VARCHAR); CREATE TABLE student (stuid VARCHAR, age INTEGER)

Question: Find the number of students who is older than 20 in each dorm.
SQL: SELECT COUNT(*), T3.dorm_name FROM student AS T1 JOIN lives_in AS T2 ON T1.stuid = T2.stuid JOIN dorm AS T3 ON T3.dormid = T2.dormid WHERE T1.age > 20 GROUP BY T3.dorm_name