SELECT ROUND(AVG(TOTAL_VALUE)) AS SA_MEDIAN
  FROM (SELECT TOTAL_VALUE
          FROM CONVENIENCE
         WHERE KIND_CODE = '100'
         ORDER BY TOTAL_VALUE DESC
         LIMIT 2 - (SELECT COUNT(*)
                      FROM CONVENIENCE) % 2
        OFFSET (SELECT (COUNT(*) - 1) / 2
                  FROM CONVENIENCE))
;