sELECT AVG(TOTAL_VALUE) AS SA_MEDIAN
FROM (
    SELECT TOTAL_VALUE
    FROM (
        SELECT TOTAL_VALUE, ROW_NUMBER() OVER (ORDER BY TOTAL_VALUE) as row, COUNT(*) OVER () as total_rows
        FROM CONVENIENCE
        where
        SURVEY_YEAR = '2019' AND
        KIND_CODE = '100'
    ) sub    
WHERE row in ((total_rows + 1) / 2, (total_rows + 2) / 2)
);