with tmp(결제일, 결제번호, 결제분류, 상품코드, 상품건수, 단가 ) as (values
('2005.01.05','S46586','판매','120124',3,5000), 
('2005.01.05','S46588','판매','120152',1,1000), 
('2005.01.07','S46592','반품','120124',-1,-5000), 
('2005.01.07','S46517','판매','120131',1,2000), 
('2005.01.11','S46526','판매','120431',1,6000), 
('2005.01.11','S46526','판매','120439',1,6000), 
('2005.01.15','S46526','판매','120431',1,6000), 
('2005.01.17','S46466','반품','120431',-1,-6000))

select 결제일, 결제번호, 결제분류, 상품코드, 상품건수, 단가
from (
select 결제일, 결제번호, 결제분류, 상품코드, 단가,
       sum(상품건수) over(PARTITION by 상품코드) 상품건수,
       rownumber() over(PARTITION by 상품코드 order by 결제일) rn
from tmp a
     )t1
where rn=1
order by 1 ;