create table #customer_payment  
  ( primary key( customer_id, payment_date), 
  customer_id int not null, payment_date datetime not null, 
  payment_amt smallmoney not null );
 
insert into #customer_payment
  ( customer_id, payment_date, payment_amt )
  values 
  ( 123, '20120112', 100.00 ),
  ( 123, '20120505', 100.00 ),
  ( 123, '20121207', 100.00 );

select sum(payment_amt)payment_amt
  from #customer_payment
    where customer_id = 123 and payment_date >= '2012-10-01';

SET LANGUAGE US_ENGLISH;
Changed language setting to us_english.
 
payment_amt
---------------------
100.00

SET LANGUAGE ITALIAN;
L'impostazione della lingua è stata sostituita con Italiano.
 
payment_amt
---------------------
300.00

Le paramètre de langue est passé à Français.
SET LANGUAGE FRENCH;
 
payment_amt
---------------------
300.00

select sum(payment_amt)payment_amt
   from #customer_payment
      where customer_id = 123 and payment_date >= '20121001';