프로그래머스 SQL : GROUP BY

프로그래머스 SQL : GROUP BY

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고양이와 개는 몇 마리 있을까

SELECT ANIMAL_TYPE,COUNT(*) FROM ANIMAL_INS
GROUP BY ANIMAL_TYPE ORDER BY ANIMAL_TYPE;

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동명 동물 수 찾기

SELECT NAME, COUNT(NAME) FROM ANIMAL_INS
GROUP BY NAME HAVING COUNT(NAME)>1 ORDER BY NAME;

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입양 시각 구하기(1)

SELECT HOUR(DATETIME) "HOUR",COUNT(*) "COUNT" FROM ANIMAL_OUTS
GROUP BY HOUR(DATETIME) HAVING HOUR BETWEEN 9 AND 20
ORDER BY HOUR(DATETIME);

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입양 시각 구하기(2)

SET @HOUR := -1;    -- =(비교연산자)와 차별하기 위한 :=(대입연산자)
SELECT (@HOUR:=@HOUR+1) "HOUR",
(SELECT COUNT(*) FROM ANIMAL_OUTS WHERE HOUR(DATETIME) = @HOUR) "COUNT"
FROM ANIMAL_OUTS WHERE @HOUR<23;

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