문제
풀이
서브 쿼리를 사용해서 풀었다.
SELECT A.ID, IFNULL(B.CHILD_COUNT, 0) AS CHILD_COUNT
FROM ECOLI_DATA AS A
LEFT JOIN (SELECT PARENT_ID, COUNT(ID) AS CHILD_COUNT
FROM ECOLI_DATA
GROUP BY PARENT_ID
HAVING PARENT_ID IS NOT NULL) AS B
ON A.ID = B.PARENT_ID
ORDER BY A.ID;
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