[SQL] 프로그래머스 [Level-4] 입양시각구하기(2)

<MySQL>

SET @HOUR = -1;
SELECT (@HOUR := @HOUR + 1) AS HOUR
     , (SELECT COUNT(HOUR(DATETIME))
          FROM ANIMAL_OUTS
         WHERE HOUR(DATETIME) = @HOUR) AS COUNT
FROM ANIMAL_OUTS
WHERE @HOUR < 23

<Oracle>

SELECT HOUR
     , COUNT(B.DATETIME) AS COUNT
  FROM (
         SELECT LEVEL-1 AS HOUR
           FROM DUAL
        CONNECT BY LEVEL <= 24
       ) A
LEFT OUTER JOIN ANIMAL_OUTS B
ON A.HOUR = TO_CHAR(B.DATETIME, 'HH24')
GROUP BY HOUR
ORDER BY HOUR

프로그래머스 입양시각구하기 SQL