https://school.programmers.co.kr/learn/courses/30/lessons/299307

정답

SELECT
    ID,
    CASE
        WHEN SIZE_OF_COLONY <= 100 THEN 'LOW'
        WHEN SIZE_OF_COLONY <= 1000 THEN 'MEDIUM'
        ELSE 'HIGH'
    END AS SIZE
FROM
    ECOLI_DATA
ORDER BY
    ID

해설

너무 간단하기 때문에 해설 생략