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, 
    sum(TOTAL_AMT),
    sum(MALE_AMT),
    sum(FEMALE_AMT)    
from population
group by District_code, District_name