[프로그래머스] 오랜 기간 보호한 동물(1)

https://school.programmers.co.kr/learn/courses/30/lessons/59044

SELECT o.NAME, o.DATETIME
from ANIMAL_OUTS o
where exists (select i.ANIMAL_ID from ANIMAL_INS i where i.ANIMAL_ID = o.ANIMAL_ID)
order by o.DATETIME
limit 3;

=>

SELECT DISTINCT i.NAME, i.DATETIME
from ANIMAL_INS i
where not exists 
(select o.ANIMAL_ID from ANIMAL_OUTS o where i.ANIMAL_ID = o.ANIMAL_ID)
order by i.DATETIME
limit 3;