MySQL 실습 | 대여 횟수가 많은 자동차들의 월별 대여 횟수 구하기

문제 1.  대여 횟수가 많은 자동차들의 월별 대여 횟수 구하기

CAR_RENTAL_COMPANY_RENTAL_HISTORY 테이블에서 대여 시작일을 기준으로 2022년 8월부터 2022년 10월까지 총 대여 횟수가 5회 이상인 자동차들에 대해서 해당 기간 동안의 월별 자동차 ID 별 총 대여 횟수(컬럼명: RECORDS) 리스트를 출력하는 SQL문을 작성해주세요. 결과는 월을 기준으로 오름차순 정렬하고, 월이 같다면 자동차 ID를 기준으로 내림차순 정렬해주세요. 특정 월의 총 대여 횟수가 0인 경우에는 결과에서 제외해주세요.

프로그래머스

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💡 문제 풀이 

`처음 풀이`

-- 서브쿼리 2개 사용
SELECT MONTH, CAR_ID, RECORDS
FROM
    (SELECT MONTH,
        CAR_ID,
        RECORDS,
        SUM(RECORDS) OVER (PARTITION BY CAR_ID) AS TOTAL
    FROM 
        (SELECT MONTH(START_DATE) AS MONTH, 
            CAR_ID, 
            COUNT(*) AS RECORDS
        FROM CAR_RENTAL_COMPANY_RENTAL_HISTORY
        WHERE MONTH(START_DATE) BETWEEN 8 AND 10
        GROUP BY MONTH, CAR_ID
        HAVING COUNT(*) != 0        
        ) t1
     ) t2
WHERE TOTAL >= 5
ORDER BY MONTH ASC, CAR_ID DESC;

 

`더 나은 풀이`

SELECT MONTH, CAR_ID, RECORDS
FROM
(
SELECT MONTH(START_DATE) AS MONTH, 
    CAR_ID, 
    COUNT(*) AS RECORDS,
    SUM(COUNT(*)) OVER (PARTITION BY CAR_ID) AS TOTAL -- 윈도우함수로 집계함수 중첩
FROM CAR_RENTAL_COMPANY_RENTAL_HISTORY
WHERE MONTH(START_DATE) BETWEEN 8 AND 10
GROUP BY MONTH, CAR_ID
HAVING COUNT(*) != 0
) t1
WHERE TOTAL >= 5
ORDER BY MONTH ASC, CAR_ID DESC

 

`오답노트`

• 윈도우 함수로 집계함수를 중첩해서 서브쿼리 2개를 -> 1개로 줄일 수 있음