WITH temp_conv AS (
    SELECT
        total_value
    FROM
        convenience
    WHERE
        survey_year = 2019
        AND kind_code = '100'
)
SELECT
    ROUND(AVG(total_value)) AS SA_MEDIAN
FROM (
    SELECT
        total_value
    FROM
        temp_conv
    ORDER BY
        total_value DESC
    LIMIT CASE
        WHEN (SELECT COUNT(1) % 2 FROM temp_conv) = 0 THEN 2
        ELSE 1
    END
    -- n_record: 6 -> 3 ~ 4
    -- n_record: 7 -> 4
    -- n_record: 8 -> 4 ~ 5
    OFFSET ( --開始位置(この行は含まない)
        SELECT 
            (COUNT(1) - 1) / 2 
        FROM 
            temp_conv
    ) 
) x