with ordered_table as (
select
  total_value as total_value,
  row_number() over (order by total_value) as row_id,
  (select count(1) from convenience) as cnt
from convenience
where survey_year = 2019 and kind_code = '100'
)
select
  avg(total_value) as SA_MEDIAN
from ordered_table
where row_id between cnt/2.0 and cnt/2.0 + 1
;