Onda ovako?
SELECT A.id_customer,A.firstname, A.lastname, A.email, A.birthday, B.phone, B.phone_mobile, B.address1, B.address2, B.postcode, B.city, C.name, SUM(D.totail_paid_real)
FROM ps_customer AS A
LEFT JOIN ps_address AS B ON ( B.id_customer = A.id_customer )
LEFT JOIN ps_country_lang AS...