select
    COUNT(user_id) AS total
FROM (
    SELECT
        user_id,
        center_id,
        start,
        trial_id,
        sign
    FROM user_results__2020 r
    WHERE status = 1
        AND IFNULL(result, "") <> ""
        AND MONTH(start) BETWEEN 1 AND 3
        AND start = (
            SELECT
                MAX(start)
            FROM user_results__2020
            WHERE user_id = r.user_id
                AND trial_id = r.trial_id
                AND center_id = r.center_id
                AND status = 1
                AND MONTH(start) BETWEEN 1 AND 3
                AND IFNULL(result, "") <> ""
            )
    ) ur;