SELECT
    ROUND(AVG(TOTAL_VALUE)) AS SA_MEDIAN
FROM
    (
        SELECT
                ROW_NUMBER() OVER (ORDER BY TOTAL_VALUE) AS P
                , TOTAL_VALUE
            FROM
                CONVENIENCE
            WHERE
                SURVEY_YEAR = 2019
                AND KIND_CODE = '100'
    ) D
    INNER JOIN (
        SELECT
                COUNT(*) N
            FROM
                CONVENIENCE
            WHERE
                SURVEY_YEAR = 2019
                AND KIND_CODE = '100'
    ) T
    ON D.P * 2 BETWEEN N AND N+2