with total_value_ord as (
select
TOTAL_VALUE
,ROW_NUMBER() OVER (ORDER BY TOTAL_VALUE DESC) as row_num
from convenience
where SURVEY_YEAR=2019
AND KIND_CODE=100
), get_row_num as (
select 
max(row_num)/2 as medium_row
,max(row_num)%2 as rest
from total_value_ord
)
select
sum(total_value)/count(0) as SA_MEDIAN
from total_value_ord
where row_num >= (select medium_row + rest from get_row_num)
and row_num <= (select case when rest=0 then medium_row+1 else medium_row + rest end from get_row_num)