WITH median AS (
SELECT
 *,
 ROW_NUMBER()OVER(ORDER BY TOTAL_VALUE) AS rank
FROM
 CONVENIENCE
WHERE
 SURVEY_YEAR = 2019
AND
 KIND_CODE = '100'
)
SELECT
 CASE
  WHEN MOD(MAX(rank)/2,0) = 1 THEN (SELECT SUM(TOTAL_VALUE) FROM median WHERE rank = (SELECT MAX(rank)/2 FROM median))
  ELSE 
  (
  SELECT 
   ROUND(SUM(TOTAL_VALUE)/2)
  FROM 
   median 
  WHERE 
   rank = ( SELECT MAX(rank)/2 FROM median)
  OR
   rank = ( SELECT (MAX(rank)/2) + 1 FROM median)
  ) 
 END AS SA_MEDIAN
FROM
 median