SELECT
    CAST(ROUND(AVG(ABS(TIMESTAMPDIFF(SECOND, o_logtime, s_logtime)))) AS SIGNED) AS gap
FROM(
    SELECT
        o.order_id,
        o.logtime AS o_logtime,
        s.logtime AS s_logtime
    FROM order_log o
    JOIN select_log s 
    ON o.order_id = s.order_id
) AS tb1