문제 링크

고양이와 개는 몇 마리 있을까

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SELECT ANIMAL_TYPE, COUNT (*) AS count
FROM ANIMAL_INS
WHERE ANIMAL_TYPE = "Cat" OR ANIMAL_TYPE = "Dog"
GROUP BY ANIMAL_TYPE

동명 동물 수 찾기

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SELECT NAME, COUNT (*) AS count
FROM ANIMAL_INS
WHERE NAME IS NOT null
GROUP BY NAME
HAVING count >= 2
ORDER BY NAME

입양 시각 구하기(1)

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SELECT HOUR(DATETIME) AS HOUR, COUNT(DATETIME) AS COUNT
FROM ANIMAL_OUTS
WHERE HOUR(DATETIME) >= 9 AND HOUR(DATETIME) <= 19
GROUP BY HOUR

입양 시각 구하기(2)

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SET @hour = -1;
SELECT (@hour := @hour + 1) AS HOUR,
  (
      SELECT COUNT(*) AS COUNT
      FROM ANIMAL_OUTS
      WHERE HOUR(DATETIME) = @hour
  )
FROM ANIMAL_OUTS
WHERE @hour < 23