PostgreSQL:区间“10天"和当前行之间的范围 [英] PostgreSQL: RANGE BETWEEN INTERVAL '10 DAY' AND CURRENT ROW

问题描述

我有一张表，用于存储每件商品的每日价格.如果价格未更新，则当天没有该商品的记录.

I have a table which stores, for every item, the daily price. If the price hasn't been updated, there isn't a record for that item on that day.

我需要编写一个查询，为每个项目检索从当前行日期起 10 天回顾窗口的最新价格，否则返回 NULL.我正在考虑使用 RANGE BETWEEN INTERVAL 语句来实现这一点.类似的东西:

I need to write a query which retrieves, for every item, the most recent price with a lookback window of 10 days from the current row date otherwise return NULL. I was thinking to achieve that using a RANGE BETWEEN INTERVAL statement. Something like:

SELECT
    DATE(datetime),
    item_id,
    LAST(price) OVER(
        PARTITION BY item_id
        ORDER BY datetime DESC
        RANGE BETWEEN INTERVAL '10 DAYS' AND CURRENT ROW
    ) AS most_recent_price_within_last_10days
FROM ...
GROUP BY
    date,
    item_id,
    price

不幸的是，这个查询引发了一个错误:

Unfortunately this query raises an error:

LINE 20:  RANGE BETWEEN INTERVAL '10 DAY' PRECEDING AND CURRENT ROW
          ^

我看到一篇旧博客文章说在 Postgres 中不可能进行这样的操作.这仍然准确吗?

I came across an old blog post saying such operation is not possible in Postgres. Is this still accurate?

推荐答案

您可以使用 ROW_NUMBER() 为每个项目提取最近 10 天内的最新记录:

You could use ROW_NUMBER() to pull out the most recent record within the last 10 days for each item:

SELECT * 
FROM (
    SELECT
        DATE(datetime),
        item_id,
        price AS most_recent_price_within_last_10days,
        ROW_NUMBER() OVER(PARTITION BY item_id ORDER BY datetime DESC) rn
    FROM ...
    WHERE datetime > NOW() - INTERVAL '10 DAY'
) x WHERE rn = 1

在子查询中，WHERE 子句对日期范围进行过滤；ROW_NUMBER() 为具有相同 item_id 的记录组中的每条记录分配一个排名，最近的记录在前.然后，外部查询只过滤行号为 1 的记录.

In the subquery, the WHERE clause does the filtering on the date range; ROW_NUMBER() assigns a rank to each record within groups of records having the same item_id, with the most recent record first. Then, the outer query just filters in records having row number 1.

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