WITH 集計データ AS (
    select 
        TOTAL_VALUE as 値
        ,count(*) as 件数
    from
        CONVENIENCE
    where 
        SURVEY_YEAR = 2019
    and 
        KIND_CODE = 100
    group by
        TOTAL_VALUE
)
, SUB AS (
  SELECT
    値
  , 件数
  , SUM(件数) OVER( ORDER BY 値) AS 累積件数
  , SUM(件数) OVER() AS 総件数
  FROM 集計データ
)

SELECT ROUND(AVG(値),0) AS SA_MEDIAN
FROM SUB
WHERE 総件数/2.0 BETWEEN 累積件数 - 件数 AND 累積件数