programmers SQL 고득점 Kit - GROUP BY 문제 코드

https://programmers.co.kr/learn/courses/30/parts/17044

1. 고양이와 개는 몇 마리 있을까

select animal_type, count(animal_type)
from animal_ins
group by animal_type
order by 1;

2. 동명 동물 수 찾기

select name, count(name)
from animal_ins
group by name
having count(name) >= 2
order by 1;

3. 입양 시각 구하기(1)

select hour(datetime) as HOUR, count(datetime) as COUNT
from animal_outs
where hour(datetime) between 9 and 19
group by hour(datetime)
order by 1;

4. 입양 시각 구하기(2)

with recursive time as (
select 0 as HOUR
Union all
select HOUR + 1 from time  where HOUR < 23)

select HOUR, count(datetime)
from time left outer join animal_outs 
on HOUR = hour(datetime)
group by HOUR
order by HOUR;