What is the first name of the candidate with login name mkou?
select first_name from people where login_name = "mkou"
Give the candidate id instead.
select t2.candidate_id from people as t1 join candidates as t2 on t1.person_id = t2.candidate_id where t1.login_name = "mkou"
Find the same for the candidate with emailstanley.monahan@example.org.
select t2.candidate_id from people as t1 join candidates as t2 on t1.person_id = t2.candidate_id where t1.email_address = "stanley.monahan@example.org"