SELECT MAX(c.name) AS "Customer",COUNT(n.customer) as "Numbers"
FROM
customers c INNER JOIN numbers n
on(n.customer=c.id)
GROUP BY c.id
HAVING count(n.customer)>0
---------------------------------------
SELECT c.name AS "Customer",Numbers
FROM (SELECT ID,Name from customers)AS c
INNER JOIN (
SELECT customer,Counr(1) AS "Numbers" from numbers GROUP BY customer)n
ON(n.customer=c.id)
WHERE Numbers<>0