SELECT ROUND(AVG(TOTAL_VALUE)) AS SA_MEDIAN
FROM (
    SELECT
        TOTAL_VALUE
    FROM
        CONVENIENCE
    WHERE
        SURVEY_YEAR = 2019
        AND KIND_CODE = 100
    ORDER BY
        TOTAL_VALUE
    -- LIMITとOFFSETを利用して、データ件数が偶数の場合は対象データを2件、奇数の場合は1件とする
    LIMIT 2 - (SELECT COUNT(*) % 2 FROM CONVENIENCE WHERE SURVEY_YEAR = 2019 AND KIND_CODE = 100)
    OFFSET (SELECT (COUNT(*)-1) / 2 FROM CONVENIENCE WHERE SURVEY_YEAR = 2019 AND KIND_CODE = 100)
);