Table schema:
CREATE TABLE activity (actid VARCHAR, activity_name VARCHAR); CREATE TABLE participates_in (stuid VARCHAR)

Question: Find the ids of the students who participate in Canoeing and Kayaking.
SQL: SELECT T1.stuid FROM participates_in AS T1 JOIN activity AS T2 ON T2.actid = T2.actid WHERE T2.activity_name = 'Canoeing' INTERSECT SELECT T1.stuid FROM participates_in AS T1 JOIN activity AS T2 ON T2.actid = T2.actid WHERE T2.activity_name = 'Kayaking'