[SQL] GROUP BY

모든 문제의 출처는 프로그래머스 SQL 고득점 KIT입니다. (https://programmers.co.kr/learn/challenges)

예제 1

TIP

• 행의 개수를 알고 싶으면 COUNT(COLUMN_NAME) 사용!

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

예제 2

code

SELECT NAME, COUNT
FROM (
    SELECT NAME, COUNT(NAME) AS COUNT
    FROM ANIMAL_INS
    GROUP BY NAME
    ) SQ1
WHERE COUNT >= 2 AND NAME IS NOT NULL
ORDER BY NAME;

예제 3

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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(DATETIME)
ORDER BY HOUR

예제 4

code