with t1 as(
select TOTAL_VALUE, row_number() over (order by TOTAL_VALUE) as rank
from CONVENIENCE
where SURVEY_YEAR = 2019 and KIND_CODE = '100'
)
-- max(rank) の偶奇で分ける
select 
-- rank
    ROUND(AVG(TOTAL_VALUE)) AS SA_MEDIAN
from t1
-- 20 -> 10 11 -> 平均 | 21 -> 10.5 11.5 -> 11
where rank between (
    select max(rank) * 1.0 / 2 from t1
    ) and (
    select max(rank) * 1.0 / 2 + 1 from t1
    )