SELECT
    username,
    SUM(consumption) AS consumption,
    CASE
        WHEN SUM(consumption) <= 200 THEN CAST(ROUND(SUM(consumption * tariff_a), 2) AS CHAR)
        ELSE 'NULL'
    END AS `A(0-200)`,
    CASE
        WHEN SUM(consumption) BETWEEN 201 AND 499 THEN CAST(ROUND(SUM(consumption * tariff_b), 2) AS CHAR)
        ELSE 'NULL'
    END AS `B(201-499)`,
    CASE
        WHEN SUM(consumption) >= 500 THEN CAST(ROUND(SUM(consumption * tariff_c), 2) AS CHAR)
        ELSE 'NULL'
    END AS `C(500+)`
FROM
    meter_readings -- Replace with your actual table name(s) or JOINs
GROUP BY
    username
ORDER BY
    username ASC;