SELECT
SUM(
CASE
WHEN int_datahora_entrada <= '2020-06-30' AND int_datahora_saida >= '2020-06-01'
THEN date_part('day', age(greatest(int_datahora_entrada, '2020-06-01'), least(int_datahora_saida, '2020-06-30')))
ELSE 0
END
) AS "06"
FROM
int_internacao
;