sqlite按总和过滤 [英] sqlite filtering by sum

问题描述

我有一个包含 1000 条记录的数据库，每行包含一个文件名和一个文件大小.如果所有文件大小的总和超过特定限制，则:- 我需要创建一个 sql 查询来删除所有剩余的行，从最旧到最新

I have a database with 1000 records containing a file name and a file size on each row. If the SUM of all file sizes exceeds a specific limit, then: - I need to create a sql query to delete all the remaining rows, from oldest to newest

有什么建议吗?谢谢

推荐答案

假设一个表是这样创建的:

Supposing a table created thus:

CREATE TABLE Files (Id INTEGER PRIMARY KEY, FileName TEXT, CreationDate DATE, Size INTEGER);

要获取运行总和，请使用以下查询:

To get the running sum, use the following query:

SELECT f1.id AS FileId, sum(f2.size) AS RunningSumSize
FROM file f1 INNER JOIN file f2
ON f1.createdDate<=f2.createdDate
GROUP BY FileId
ORDER BY RunningSumSize DESC;

要删除超过阈值的文件 ID:

To delete the file ID's above the threshold:

DELETE FROM File WHERE Id IN
 (SELECT FileId FROM 
  (SELECT f1.id AS FileId, sum(f2.size) AS RunningSumSize
  FROM file f1 INNER JOIN file f2
  ON f1.createdDate<=f2.createdDate
  GROUP by FileId
  ORDER by RunningSumSize DESC)
  WHERE RunningSumSize > :ThresholdSize:);

注意:order by 是可选的.

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