What are the enrollment dates of all the tests that have result "Pass"?
select t1.date_of_enrolment from student_course_enrolment as t1 join student_tests_taken as t2 on t1.registration_id = t2.registration_id where t2.test_result = "Pass"
What are the student IDs of students who passed the test?
select t1.student_id from student_course_enrolment as t1 join student_tests_taken as t2 on t1.registration_id = t2.registration_id where t2.test_result = "Pass"
How many students passed the test?
select count ( t1.student_id ) from student_course_enrolment as t1 join student_tests_taken as t2 on t1.registration_id = t2.registration_id where t2.test_result = "Pass"