CREATE TABLE groups (group_id NUMBER, activity_id number);
INSERT INTO groups (group_id, activity_id) values (1,1);
INSERT INTO groups (group_id, activity_id) values (1,2);
INSERT INTO groups (group_id, activity_id) values (2,1);
INSERT INTO groups (group_id, activity_id) values (2,2);
INSERT INTO groups (group_id, activity_id) values (2,3);