WITH jam_data AS (
    /* TRUE JAM COUNTS PER DEVICE */
    SELECT 
        Name,
        COUNT(*) AS Jam_count
    FROM
    (
        /* AREA JAMS */
        SELECT 
            Name,
            t_stamp
        FROM jam_area
        WHERE t_stamp BETWEEN :starttime AND :endtime

        UNION ALL

        /* DEVICE JAMS – EDGE DETECT */
        SELECT
            Name,
            t_stamp
        FROM
        (
            SELECT
                Name,
                t_stamp,
                Jam,
                IF(@lastName = Name, @prevJam, 0) AS prevJam,
                @prevJam := Jam,
                @lastName := Name
            FROM lane_data
                JOIN (SELECT @prevJam := 0, @lastName := '') AS vars
            WHERE t_stamp BETWEEN :starttime AND :endtime
            ORDER BY Name, t_stamp
        ) AS x
        WHERE Jam = 1 AND prevJam = 0
    ) all_jams
    GROUP BY Name
),

total AS (
    SELECT SUM(Jam_count) AS Total_jams
    FROM jam_data
)

SELECT 
    jd.Name,
    ROUND((jd.Jam_count / t.Total_jams) * 100, 2) AS Jam_percentage
FROM jam_data jd
JOIN total t
WHERE t.Total_jams > 0

UNION ALL

/* FALLBACK IF NOTHING EXISTS */
SELECT
    'N/A' AS Name,
    0 AS Jam_percentage
WHERE NOT EXISTS (
    SELECT 1 FROM jam_data
)

ORDER BY Jam_percentage DESC;