SELECT
    id,
    issue,
    delivery,
    proforma,
    restoration,
    deleted,
    IFNULL(delivery, issue) AS DATE,
    totalPrice totalPrice,
    ROUND(totalPrice * (1 - discount / 100), 2) AS discountPrice,
    (
    SELECT SUM(payment.price) SUM FROM payment
    WHERE payment.invoice_id = invoice.id
    ) payment_sum
FROM invoice
WHERE invoice.deleted = 0 AND invoice.user_id = 25
HAVING invoice.DATE BETWEEN '2014-05-01' AND '2014-05-31'
ORDER BY invoice.issue DESC