Create temporary view po2 as
select
    PF_CODE,
    SUM(CASE WHEN SURVEY_YEAR=2015 THEN TOTAL_AMT ELSE 0 END) as TA2015,
    SUM(CASE WHEN SURVEY_YEAR=2020 THEN TOTAL_AMT ELSE 0 END) as TA2020
from
    POPU_TRANSITION
WHERE
    SURVEY_YEAR IN (2015,2020)
group by
    PF_CODE;

select
    p.PF_CODE as 都道府県コード,
    pf.PF_NAME as 都道府県名,
    p.TA2015 as 総人口2015年,
    p.TA2020 as 総人口2020年,
    round(p.TA2020*100/p.TA2015) as  人口増加率
from
    po2 as p
    inner join
    PREFECTURE as pf
    on p.PF_CODE = pf.PF_CODE
order by
    人口増加率 DESC,
    都道府県コード