select
    district_code as DISTRICT_CODE,
    case when coalesce(district_name,'')='' then '不明' else district_name end as DISTRICT_NAME,
    sum(total_amt) as TOTAL_AMT,
    sum(male_amt) as MALE_AMT,
    sum(female_amt) as FEMALE_AMT
from
    population
group by
    district_code,
    case when coalesce(district_name,'')='' then '不明' else district_name end