할인율, 판매가, 이익률 계산

select c.cate1 ,
round(sum(cast(discount as numeric)) / sum(gmv) *100 , 0) || '%' as discount_rate,
sum(gmv - discount) as paid_amount,
round(sum(cast(product_profit as numeric)) / sum(gmv) *100, 0) ||'%' as product_margin,
round(sum(cast(total_profit as numeric)) / sum(gmv) *100 , 0) || '%' as total_margin
from online_order oo 
join item i on oo.itemid = i.id 
join category c on i.category_id  = c.id 
group by 1
order by 3 desc 
;

as 중요
cast(~ as varchar) -> 숫자를 문자로
cast(~ as numeric) ->  소수 변환
분자 분모 sum으로 묶어야함.
round 는 절삭을 위해 사용 -> ,0 안붙여도댐
||'%' 뒤에 %를 붙이기 위해