psql rank row

rank() OVER (PARTITION BY f1 ORDER BY f2 DESC) 

ROW_NUMBER() () OVER (PARTITION BY f1 ORDER BY f2 DESC) 
为每个匹配的f1字段生成一个行号，并按照f2排序

例子
select DID,customerID,totalPrice,ROW_NUMBER() over(order by totalPrice) as rows from OP_Order

可以用户讲多列的数据排序后横向比较，例如，oe的一个询价单，向多个供应商询价后，需要取前3个供应商价格横列显示。

select 
        product_id,
        product_qty,
        max(part1) as parter1,
        max(price1) as price1,
        max(part2) as parter2,
        max(price2) as price2,
        max(part3) as parter3,
        max(price3) as price3
from(
        select  
                product_id, product_qty,
                case  when  abc=1 then partner_id end as part1,
                case  when  abc=2 then partner_id end as part2,
                case  when  abc=3 then partner_id end as part3,
                case  when  abc=1 then price_unit end as price1,
                case  when  abc=2 then price_unit end as price2,
                case  when  abc=3 then price_unit end as price3
        from (
                select 
                        pol.id, pol.product_id, pol.partner_id, product_qty , pol.price_unit,
                        rank() OVER (PARTITION BY pol.product_id order by pol.partner_id) as abc 
                        from 
                                purchase_requisition as rq
                                left join purchase_order as po on  (po.requisition_id = rq.id)
                                left join purchase_order_line as pol on (pol.order_id = po.id)
                        where rq.id = 44
              ) as t
    ) as tt group by product_id,product_qty

结果如下：