SELECT
    *
FROM
    (
        SELECT
            companyname,
            customers.customerid,
            COUNT(jobnumber) AS number_of_jobs
        FROM
            orders
        INNER JOIN
            customers
        ON
            customers.customerid = orders.customerid
        WHERE
            (customers.group_company_id=1)
        GROUP BY
            companyname,
            customers.customerid
    )
GROUP BY
    LOWER(companyname)
HAVING
    COUNT(DISTINCT customers.customerid) > 1
ORDER BY
    companyname;