วันที่ลงทะเบียนของการทดสอบทั้งหมดที่มีผล "ผ่าน" คือเมื่อใด
What are the enrollment dates of all the tests that have result "Pass"?
df_tests = pd.DataFrame(columns=['registration_id', 'test_result']); df_enrollment = pd.DataFrame(columns=['date_of_enrolment', 'registration_id'])
df_enrollment[df_enrollment['registration_id'].isin(df_tests.loc[df_tests['test_result'] == 'Pass', 'registration_id'])]['date_of_enrolment']