mysql 表如何设置阈值或限制? [英] How do you make a threshold or limit mysql table?

问题描述

我有一个表，我只想要 20 个最近的条目，因为该表每 0.50 秒添加一行.

I have a table which i would like only to have the 20 most recent entries, because the table is adding a row every .50 seconds.

我将如何在查询数据库(mysql)时完成此操作.

How would I accomplish this in querying to the database(mysql).

每当我想推入一个新值时，我是否应该添加一个新行并删除最旧的行?

Should i add a new row and delete the oldest whenever i want to push a new value in?

推荐答案

您可以创建一个 查看.为了保证按最近排序，请引入一个带有时间戳的列作为排序依据(或者在使用顺序编号时使用主键，例如 AUTO_INCREMENT).

You could create a view. To guarantee ordering by recentness, introduce a column with a timestamp to order by (or use the primary key when using sequential numbering, such as AUTO_INCREMENT).

CREATE VIEW latest_entries AS 
SELECT ... FROM TABLE foo ORDER BY created_time LIMIT 20;

另外，不要忘记不时清理"底层表.

Also, don't forget to 'clean' the underlying table from time to time.

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