SQL - 筛选数据仅显示更改历史记录

Question

我有一个 table 看起来像：

    
 | ID_Product | Product | Price |           Date            | 
------------------------------------------------------
 |     01     |  Socks  |    |  2020-06-02 18:27:49.000  | 
 |     03     |  Belt   |    |  2020-06-03 13:27:08.000  | 
 |     01     |  Socks  |    |  2020-06-11 17:00:04.000  | 
 |     02     |  Boots  |    |  2020-06-12 09:27:19.000  | 
 |     02     |  Boots  |    |  2020-06-17 11:27:10.000  | 
 |     01     |  Socks  |    |  2020-06-25 15:29:45.000  | 
 |     01     |  Socks  |    |  2020-07-08 16:27:30.000  | 

我需要一个查询来按价格和日期获取不同的行，以获取一些价格变化的“历史记录”，就像这样

    
 | ID_Product | Product | Price |           Date            | 
------------------------------------------------------
 |     03     |  Belt   |    |  2020-06-03 13:27:08.000  | 
 |     01     |  Socks  |    |  2020-06-11 17:00:04.000  | 
 |     02     |  Boots  |    |  2020-06-17 11:27:10.000  | 
 |     01     |  Socks  |    |  2020-06-25 15:29:45.000  | 
 |     01     |  Socks  |    |  2020-07-08 16:27:30.000  | 

谢谢！

Answer 1

您似乎只想要每个产品价格的最新日期：

select product_id, price, max(date)
from t
group by product_id, price;

我以为您想知道新价格何时开始生效。为了那个原因， 您可以使用 lag() 查看价格何时变化 - 并仅保留这些行：

select t.*
from (select t.*,
             lag(price) over (partition by product_id order by date) as prev_price
      from t
     ) t
where prev_price is null or prev_price <> price;