SQL - 找到正确的值

Question

我遇到了这个问题

在此表中，我为每个金额注册了相对折扣

Amount   Discount
 500        5%
1000       10%
1200       11%
2100       15%

ecc...

在另一个表中，我得到了订单的总价，例如 2000，我如何才能找到该订单的正确折扣？在那种情况下 11% 因为 2100 > 2000 ?

Answer 1

与top:

select top 1 Discount 
from Discounts
where Amount <= 2000
order by Amount desc

Answer 2

select discount
  from tq84_discount
 where amount = (
  select max(amount)
   from tq84_discount
  where amount <= 2000
 );

测试数据：

create table tq84_discount (
  amount number,
  discount number
);

insert into tq84_discount values (  0, 0);
insert into tq84_discount values (500, 5);
insert into tq84_discount values (100, 10);
insert into tq84_discount values (1200, 11);
insert into tq84_discount values (2100, 15);

Answer 3

select top 1 Discount
from Discounts
where Amount < GrossPrice
orderby Amount desc

这个简单的查询有效。 GrossPrice 是它具有来自其他表的值的变量。在这种情况下是 2000 年。