获取最旧的修改价格

【问题标题】：Get oldest modified price获取最旧的修改价格
【发布时间】：2021-07-08 15:01:14
【问题描述】：

我有一个表格，其中每行包含 YYYYMMDD 格式的产品 ID (A)、价格 (P) 和修改日期 (D)。

这是表格：

WITH temp_table AS (
select 744583 as a, 9.21 as p, 20210706 as d from sysibm.sysdummy1
union all
select 744583 as a, 9.21 as p, 20210630 as d from sysibm.sysdummy1
union all
select 744583 as a, 9.21 as p, 20210628 as d from sysibm.sysdummy1
union all
select 744583 as a, 9.04 as p, 20210604 as d from sysibm.sysdummy1
union all
select 744583 as a, 9.04 as p, 20210201 as d from sysibm.sysdummy1
union all
select 744583 as a, 9.21 as p, 20200407 as d from sysibm.sysdummy1
)
select *
from temp_table

what i have

我想要的是价格最后一次变化的时候。在本例中，第三行： enter image description here

你会怎么做？

谢谢，

【问题讨论】：

标签： sql db2

【解决方案1】：

一种方法使用lag()然后排序：

select t.*
from (select t.*,
             lag(p) over (order by d desc) as prev_p
      from temp_table  t
     ) t
where prev_p is null or prev_p <> p
order by d desc
fetch first 1 row only;

如果您想同时为多个as 执行此操作，则有不同的方法。一个有趣的使用不同的行号：

select a, p, min(date)
from (select t.*,
             row_number() over (partition by a order by date desc) as seqnum,
             row_number() over (partition by a, p order by date desc) as seqnum_2
      from temp_table t
     ) t
where seqnum = seqnum_2
group by a, p;

您可以调查为什么会这样。这两个行号仅对于每个 a 的最后一个价格是相同的。

【讨论】：