select
    DISTRICT_CODE,
    CASE WHEN DISTRICT_NAME IS NULL
         THEN '不明'
         WHEN DISTRICT_NAME = ''
         THEN '不明'
         ELSE DISTRICT_NAME
    END as DISTRICT_NAME,
    TOTAL_AMT,
    MALE_AMT,
    FEMALE_AMT
from
    POPULATION
GROUP BY
    DISTRICT_CODE;