[Oracle] 프로그래머스 SQL 고득점 Kit - GROUP BY

https://programmers.co.kr/learn/courses/30/lessons/59040

코딩테스트 연습 - 고양이와 개는 몇 마리 있을까

SELECT ANIMAL_TYPE, COUNT(*)
FROM ANIMAL_INS
GROUP BY ANIMAL_TYPE
HAVING ANIMAL_TYPE IN ('Cat', 'Dog')
ORDER BY ANIMAL_TYPE;

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https://programmers.co.kr/learn/courses/30/lessons/59041

코딩테스트 연습 - 동명 동물 수 찾기

SELECT *
FROM (
    SELECT NAME, COUNT(NAME) CNT
    FROM ANIMAL_INS
    GROUP BY NAME
    ) T
WHERE CNT >= 2
ORDER BY NAME;

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https://programmers.co.kr/learn/courses/30/lessons/59412

코딩테스트 연습 - 입양 시각 구하기(1)

SELECT HOUR, COUNT(*)
FROM
    (SELECT TO_CHAR(DATETIME,'HH24') AS HOUR
    FROM ANIMAL_OUTS)
WHERE HOUR BETWEEN 09 AND 19
GROUP BY HOUR
ORDER BY HOUR;

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https://programmers.co.kr/learn/courses/30/lessons/59413

코딩테스트 연습 - 입양 시각 구하기(2)

SELECT DATETIME, COUNT(*)-1
from (SELECT TO_NUMBER(TO_CHAR ( LEVEL ))-1 as DATETIME FROM DUAL CONNECT BY LEVEL <= 24
      union all
      select TO_NUMBER(TO_CHAR (DATETIME,'HH24')) from ANIMAL_OUTS) 
group by DATETIME
order by DATETIME;