sql - 只在表中保留用户的最后 5 个搜索结果

Question

我需要将用户的最后 5 个搜索结果保存在一个表中。
我写了一个脚本来删除其他行，但它不起作用:

DELETE FROM         
    SELECT
        ROW_NUMBER () OVER (ORDER BY search_time DESC) AS row_number;
    FROM
        history_user
    WHERE
        user_id = 188
WHERE row_number>5

我做错了什么？

Answer 1

正确的语法 as detailed in the manual :

DELETE FROM history_user h
USING (
    SELECT pk_id, row_number() OVER (ORDER BY search_time DESC) AS rn;
    FROM   history_user
    WHERE  user_id = 188
    ) sub
WHERE sub.rn > 5
AND   h.pk_id = sub.pk_id;

pk_id 是唯一 的任何(组合)列。在您的情况下可能是 user_id、search_time - 或者，更方便的是代理主键。

对于单个 user_id，您可以简化为:

DELETE FROM history_user h
USING (
    SELECT pk_id
    FROM   history_user
    WHERE  user_id = 188
    ORDER  BY search_time DESC
    OFFSET 5
    ) sub
WHERE h.pk_id = sub.pk_id;

另一方面，要同时处理多个用户，您需要将PARTITION BY 添加到您的窗口函数中:

DELETE FROM history_user h
USING (
    SELECT pk_id, row_number() OVER (PARTITION BY user_id
                                     ORDER BY search_time DESC) AS rn;
    FROM   history_user
    ) sub
WHERE sub.rn > 5
AND   h.pk_id = sub.pk_id;