MySQL：仅在满足条件时更新字段

本文介绍了MySQL：仅在满足条件时更新字段的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

是否可以在MySQL中执行UPDATE查询，只有在满足某些条件时才更新字段值？这样的事情：

Is it possible to do an UPDATE query in MySQL which updates field value only if certain condition is met? Something like this:

UPDATE test SET CASE WHEN true THEN field = 1 END WHERE id = 123

换句话说：

UPDATE test SET something = 1, /*field that always gets updated*/ CASE WHEN true THEN field = 1 /*field that should only get updated when condition is met*/ END WHERE id = 123

这样做的正确方法是什么？

What is the proper way to do this?

推荐答案

是的！

这里有另一个例子：

UPDATE prices SET final_price= CASE WHEN currency=1 THEN 0.81*final_price ELSE final_price END

这是因为MySQL没有更新行，如果没有变化，如文档中所述：

This works because MySQL doesn't update the row, if there is no change, as mentioned in docs:

如果将列设置为当前值，则MySQL会注意到此并且不会更新它。

If you set a column to the value it currently has, MySQL notices this and does not update it.