一键执行MySQL UPDATE和SELECT [英] MySQL UPDATE and SELECT in one pass

问题描述

我有一个要执行的MySQL任务表，每一行都有一个任务的参数.
有许多工作人员应用程序(可能在不同的计算机上)，可以循环执行任务.
这些应用程序使用MySQL的本地C API访问数据库.

I have a MySQL table of tasks to perform, each row having parameters for a single task.
There are many worker apps (possibly on different machines), performing tasks in a loop.
The apps access the database using MySQL's native C APIs.

为了拥有任务，应用程序需要执行以下操作:

In order to own a task, an app does something like that:

• 生成一个全局唯一的ID(为简单起见，它是一个数字)

• Generate a globally-unique id (for simplicity, let's say it is a number)

UPDATE tasks
SET guid = %d
WHERE guid = 0 LIMIT 1

UPDATE tasks
SET guid = %d
WHERE guid = 0 LIMIT 1

SELECT params
FROM tasks
WHERE guid = %d

SELECT params
FROM tasks
WHERE guid = %d

如果最后一个查询返回一行，则表明我们拥有该行并具有要运行的参数

If the last query returns a row, we own it and have the parameters to run

是否可以通过一次调用服务器来实现相同的效果(即拥有"一行并获取其参数)?

Is there a way to achieve the same effect (i.e. 'own' a row and get its parameters) in a single call to the server?

推荐答案

尝试这样

UPDATE `lastid` SET `idnum` =  (SELECT `id` FROM `history` ORDER BY `id` DESC LIMIT 1);

上面的代码对我有用

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