Joining two tables using third as linking table, including null entries

Try left join:

select    account.bill_acct,    account.status,    account.remarks,    stage.account_classfrom    registration_account account    left join registration_profile profile            on account.profile_id = profile.reg_prof_id    left join acct_stg stage            on stage.ecpd_profile_id = profile.ecpd_profile_id                and stage.bill_acct = account.bill_acctwhere    profile.ecpd_profile_id = ?

As you want to extract all the information independent on stage table(no matches on stage table), the best suitable to use LEFT JOIN in following way:

SELECT    account.bill_acct,    account.status,    account.remarks,    stage.account_classFROM    registration_account account        JOIN registration_profile profile            ON account.profile_id = profile.reg_prof_id       LEFT JOIN acct_stg stage            ON stage.ecpd_profile_id = profile.ecpd_profile_id                and stage.bill_acct = account.bill_acctWHERE    profile.ecpd_profile_id = ?

LEFT JOIN returns all records from the left table or all record before LEFT JOIN, even if there are no matches in the right table.