정답
1. 고양이와 개는 몇 마리 있을까
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select ANIMAL_TYPE, count(ANIMAL_TYPE) as count from ANIMAL_INS
group by ANIMAL_TYPE
order by ANIMAL_TYPE asc;
2. 동명 동물 수 찾기
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select NAME, count(NAME) as COUNT from ANIMAL_INS
group by NAME
having NAME != 'NULL' and count(NAME) > 1
order by NAME asc;
3. 입양 시각 구하기(1)
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select hour(DATETIME) as HOUR, count(DATETIME) as COUNT
from ANIMAL_OUTS
group by hour(DATETIME)
having hour >= 9 and hour < 20
order by hour asc;
4. 입양 시각 구하기(2)
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set @hour := -1;
select (@hour := @hour+1) as HOUR,
(select count(*) from ANIMAL_OUTS
where hour(DATETIME) = @hour) as COUNT
from ANIMAL_OUTS
where @hour < 23;