with subq as (
    select count(*)
    from convenience
    where survey_year = 2019
      and kind_code = '100'
)

,subq2 as (
select *,row_number() over (order by total_value) as row
from convenience
    where survey_year = 2019
      and kind_code = '100'
)
select avg(total_value)
from subq2

where row in ( (cast((select * from subq) as float) /2) 
              ,(cast((select * from subq) as float) /2) +1, 
               (cast((select * from subq) as float) /2) +0.5
             )