SELECT
DISTRICT_CODE AS '地区コード',
CASE
    WHEN DISTRICT_NAME IS NULL THEN '不明'
    WHEN DISTRICT_NAME = '' 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;