SELECT
    DISTRICT_CODE AS 地区コード,
    CASE 
        WHEN DISTRICT_NAME = '' THEN '不明'
        WHEN DISTRICT_NAME IS NULL THEN '不明'
        ELSE DISTRICT_NAME
    END AS 地区名,
    TOTAL_AMT AS 総数,
    MALE_AMT AS 男性数,
    FEMALE_AMT AS 女性数
FROM 
    POPULATION