openpbx=> select * from subscriptions where user_id = '1'; 
id | user_id | product_id |          created_at           | deleted_at 
----+---------+------------+-------------------------------+------------
  1 |       1 |          1 | 2006-12-02 15:03:36.637406+01 | 
  2 |       1 |          1 | 2006-12-02 15:03:36.637406+01 | 
  3 |       1 |          2 | 2006-12-02 15:03:36.637406+01 | 
(3 rows)


openpbx=> INSERT INTO subscriptions_billed(user_id,product_id,invoice_id) SELECT subscriptions.user_id,product_id,MAX(invoices_temp.id) FROM subscriptions,invoices_temp WHERE subscriptions.user_id = 1 AND invoices_temp.user_id = 1 GROUP BY subscriptions.user_id,subscriptions.product_id;
INSERT 0 2
openpbx=> select * from subscriptions_billed; 
id | user_id | product_id | start_date | end_date | invoice_id 
----+---------+------------+------------+----------+------------
 48 |       1 |          2 |            |          |         31
 49 |       1 |          1 |            |          |         31
(2 rows)