如何创建一个循环通过PostgreSQL中的另一个函数的函数？

select COUNT(up.*) as "Total Upsell Accounts in October" from 
list_all_upsells('2015-10-01 00:00:00'::timestamp,'2015-10-31 23:59:59'::timestamp) as up
where up.user_id not in
(select distinct user_id from paid_users_no_more 
where concat(extract(month from payment_stop_date),'-',extract(year from payment_stop_date))<>
concat(extract(month from payment_start_date),extract(year from payment_start_date)));

list_all_upsells过程如下所示：

DECLARE
payor_email_2 text;
   BEGIN
FOR payor_email_2 in select distinct payor_email from paid_users LOOP
return query
execute
'select paid_users.* from paid_users,(
select payment_start_date as first_time from paid_users
where payor_email = $3
order by payment_start_date limit 1
) as dummy
where payor_email = $3
and payment_start_date > first_time
and payment_start_date between $1 and $2
and first_time < $1'
using a,b,payor_email_2;
END LOOP;
return;
END

我想能够在我们有记录的所有月份运行这个并在一个表中查询数据,如下所示：

Month   | Total Upselled Accounts
---------------------------------
08/2014 | 23
09/2014 | 35
ETC...
10/2015 | 56

我有一个问题是抓住每个月的第一个月和每个月的最后一个月我们经营的月份：

select distinct date_trunc('month',payment_start_date)::date as startmonth
from paid_users ORDER BY startmonth;

上个月：

SELECT distinct (date_trunc('MONTH',payment_start_date) + 
INTERVAL '1 MONTH - 1 day')::date as endmonth from paid_users 
ORDER BY endmonth;

现在,我将如何创建一个循环list_all_upsells的函数并获取这几个月中的每一个的计数？即startmonth的第一个查询给了我2014-03-01,2014-04-01,…到2015-10-01,而endmonth的第二个查询给了我2014-03-31,2014-04-30,.. .to 2015-10-31.我想在这几个月的每个月运行list_all_sells,这样我就可以每个月得到一个总计数我们拥有多少外包帐户

我的paid_users表看起来像这样：

CREATE TABLE paid_users
(
  user_id integer,user_email character varying(255),payor_id integer,payor_email character varying(255),payment_start_date timestamp without time zone DEFAULT now()
)

paid_users_no_more：

CREATE TABLE paid_users_no_more
(
  user_id integer,payment_stop_date timestamp without time zone DEFAULT now()
)