select
    PO.PF_CODE as '都道府県コード',
    PF.PF_NAME as '都道府県名',
    PO.TOTAL_AMOUNT as '総人口2015年',
    PO20.TOTAL_AMOUNT as '総人口2020年'
    
from
    POPU_TRANSITION as PO
    inner join PREFECTURE as PF
        on PO.PF_CODE = PF.PF_CODE

    inner join POPU_TRANSITION as PO20
        on PO.PF_CODE = PF.PF_CODE
        and PO20.SURVEY_YEAR = 2020