If you have a forced heirchy and can use outer joins i would use a command to outer join them join them together using a case statment to drop the last letter and join on that field (I'll call it PrimaryID).

What are your 3 queries?

select c.client_code,sh.change_date, c.client_name, '1TRAN' || ecf.client_field_data || 'C'

from event e, status_history sh, event_client_field ecf, client c

where e.event_id = sh.event_id

and e.event_id = ecf.event_id(+)

and e.client_id = c.client_id

and ecf.client_field_name = 'CLIENT LOSS IDENTIFIER'

and e.client_id = 3180

and sh.current_status_code = e.event_status_code

and sh.event_case_id is null

and sh.current_status_code in ('REJECTAPPR', 'CLOSEAPPR')

and (e.reject_code not in ('A/O-BR REJ', 'BRANCH REJ') or

e.reject_code is null)

and trunc(sh.change_date) = trunc(sysdate -1)

from event_client_field ecf, event e, client c

where e.event_id = ecf.event_id(+)

and e.client_id = c.client_id

and ecf.client_field_name = 'CLIENT LOSS IDENTIFIER'

and e.client_id = 3180

and e.event_status_code = 'OPEN'

and trunc(e.created_date) = trunc(sysdate)-1

from event_client_field ecf, event e, client c

where e.event_id = ecf.event_id(+)

and e.client_id = c.client_id

and ecf.client_field_name = 'CLIENT LOSS IDENTIFIER'

and e.client_id = 3180

and e.event_status_code = ('WAREHOUSE')

and trunc(e.created_date) = trunc(sysdate -1)