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