Hay varias formas de obtener el registro más antiguo y evitar tener que escribir el mismo criterio dos veces.
Uso de FETCH FIRST ROWS (disponible a partir de Oracle 12c)
select *
from abc_customer_details cd
join abc_customers c on c.id = cd.customer_id
where cd.country_code = 'KE'
order by creation_timestamp
fetch first row only;
Uso de una cláusula CTE (WITH)
with cte as
(
select *
from abc_customer_details cd
join abc_customers c on c.id = cd.customer_id
where cd.country_code = 'KE'
)
select *
from cte
where (creation_timestamp) = (select min(creation_timestamp) from cte);
Uso de funciones de ventana
select *
from
(
select cd.*, c.*, min(creation_timestamp) over () as min_creation_timestamp
from abc_customer_details cd
join abc_customers c on c.id = cd.customer_id
where cd.country_code = 'KE'
)
where creation_timestamp = min_creation_timestamp;
(Por cierto, cambié los criterios de unión en todas estas consultas. Parece extremadamente improbable que desee unirse en abc_customer_details.id = abc_customers.customer_id .)
