[프로그래머스] GROUP BY: 입양 시각 구하기(2)*

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

프로그래머스

 

제출 코드

SELECT 
    TIME_ZONE.HOUR,
    IFNULL(COUNT(O.ANIMAL_ID), 0) AS 'COUNT'
FROM 
    (SELECT 0 AS 'HOUR' UNION
     SELECT 1 UNION
     SELECT 2 UNION
     SELECT 3 UNION
     SELECT 4 UNION
     SELECT 5 UNION
     SELECT 6 UNION
     SELECT 7 UNION
     SELECT 8 UNION
     SELECT 9 UNION
     SELECT 10 UNION
     SELECT 11 UNION
     SELECT 12 UNION
     SELECT 13 UNION
     SELECT 14 UNION
     SELECT 15 UNION
     SELECT 16 UNION
     SELECT 17 UNION
     SELECT 18 UNION
     SELECT 19 UNION
     SELECT 20 UNION
     SELECT 21 UNION
     SELECT 22 UNION
     SELECT 23) AS TIME_ZONE
LEFT JOIN ANIMAL_OUTS AS O
 ON HOUR(O.DATETIME) = TIME_ZONE.HOUR
GROUP BY 1
ORDER BY 1