SELECT StuID FROM Participates_in INTERSECT SELECT StuID FROM Student WHERE age  <  20
What are the ids of the students who are under 20 years old and are involved in at least one activity.
SELECT StuID FROM Participates_in INTERSECT SELECT StuID FROM Student WHERE age < 20
select stuid from participates_in intersect select stuid from student where age < value
What are the ids of the students who are under 20 years old and are involved in at least one activity .