show the login name and password for registration id  2
select T1.login_name, T1.password from students AS T1 JOIN Student_Course_Enrolment AS T2 ON T2.student_id = T1.student_id WHERE registration_id = 2
login name and password for a given registration id refers to joining students table with Student_Course_Enrolment table on student_id and filtering the result where registration_id = 2;