with ordered as (
  select
      TOTAL_VALUE,
      row_number() over (order by TOTAL_VALUE) as row_id,
      (select count(1) from CONVENIENCE
        where SURVEY_YEAR = 2019
          and KIND_CODE = '100'
        ) as ct
  from CONVENIENCE
  where SURVEY_YEAR = 2019
  and KIND_CODE = '100'
)

select round(avg(TOTAL_VALUE)) as median
from ordered
where row_id between ct/2.0 and ct/2.0 + 1
;