SELECT wer.last_name

FROM (SELECT i.customer_id, cl.last_name,

       CAST(i.invoice_date AS date)

FROM invoice as i

LEFT JOIN client as cl on cl.customer_id= i.customer_id

WHERE EXTRACT(MONTH FROM CAST(i.invoice_date AS date)) = 1 AND EXTRACT(YEAR FROM CAST(i.invoice_date AS date)) = 2013

GROUP BY i.customer_id,CAST(i.invoice_date AS date),cl.last_name) as der

LEFT OUTER JOIN

(SELECT cl.last_name,cl.customer_id,CAST(i.invoice_date AS date)

FROM client as cl

LEFT JOIN invoice as i on i.customer_id=cl.customer_id

WHERE EXTRACT(YEAR FROM CAST(i.invoice_date AS date)) = 2013 and EXTRACT(MONTH FROM CAST(i.invoice_date AS date)) <> 1

GROUP BY cl.last_name,cl.customer_id,CAST(i.invoice_date AS date)) as wer on wer.customer_id = der.customer_id

GROUP BY wer.last_name