CREATE TEMPORARY VIEW available_campaigns AS

      -- all subscribed campaigns of the given ad type
      SELECT campaigns.id 
        FROM campaigns
        INNER JOIN subscriptions
          ON subscriptions.campaign_id = campaigns.id
         AND subscriptions.site_id = v_site_id
        WHERE campaigns.ad_type = v_ad_type

      -- exclude banned campaigns
      EXCEPT
      SELECT actions.campaign_id
        FROM actions
        INNER JOIN campaigns
          ON campaigns.id = actions.campaign_id
         AND campaigns.pay_per = v_action
         AND actions.address = v_address
         AND now() - actions.created_at < campaigns.reload_ban;

    SELECT campaigns.id 
      INTO a_campaign_id
      FROM available_campaigns AS campaigns 
      ORDER BY random() LIMIT 1;