with RAN as(
select
PF_CODE
,TOTAL_VALUE
,rank() over(order by TOTAL_VALUE) AS RK
from CONVENIENCE
where SURVEY_YEAR=2019 and KIND_CODE=100 
)
,AV as(
select 
AVG(RK) AS AVG_RANK
from RAN
)

select
round(avg(TOTAL_VALUE)) as SA_MEDIAN
from RAN
    cross join AV
where RK-AVG_RANK between 0 and 0.5 or AVG_RANK-RK between 0 and 0.5