Question

我需要将用户的最后5个搜索结果保留在表格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。在你的情况下可能是user_id，search_time - 或者更方便的是代理主键。

对于单 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;

在表格中仅保留用户的最后5个搜索结果

1 个答案: