select round(avg(TOTAL_VALUE)) as SA_MEDIAN
from(
    select SURVEY_YEAR,  PF_CODE, KIND_CODE, TOTAL_VALUE,
        row_number() over (partition by SURVEY_YEAR order by TOTAL_VALUE) as rownum, --TOTAL_VALUE順の連番
        count(*) over (partition by SURVEY_YEAR) as year_cnt,         --SURVEY_YEAR単位の件数
        count(*) over (partition by SURVEY_YEAR) / 2.0 as year_center --SURVEY_YEAR単位の件数 / 2.0 (小数点も出すため、2.0)
    from CONVENIENCE
    where SURVEY_YEAR = 2019
     and KIND_CODE = '100'
)
where rownum between round(year_center) and round(year_center+0.5)