任何方式将值从一个单元格传输到另一个？ [英] Any way to transfer value from one cell to another?

问题描述

在SQL语言或MySQL（或其他DBMA）中有什么方法可以将值从一个单元传输到另一个单元？例如，假设有一个名为user_cars的表具有以下结构：

Is there any way in the SQL language or in MySQL (or other DBMA) to transfer a value from one cell to another? For example, say there is a table called user_cars with the following structure:

|id| |user_name| |num_cars|

Bob有5辆车，John有3辆车。有没有办法在一个查询减去2车从鲍勃和添加2到约翰？我知道这可以用两个更新查询，但我只想知道是否有更有效的方式。

Bob has 5 cars, and John has 3 cars. Is there any way to in one query subtract 2 cars from Bob and add 2 to John? I know this can be done with two update queries, but I'd just like to know if there was a more efficient way.

推荐答案

对于Oracle，你可以这样做。不知道在mysql中是否有等价的。显然，这个特定的语句非常特定于你所说的例子。

For Oracle you could do this. Don't know if there is an equivalent in mysql. Obviously this particular statement is very specific to the example you stated.

 UPDATE user_cars
   SET num_cars = num_cars +
                     CASE WHEN user_name='Bob' THEN -2
                          WHEN user_name='John' THEN +2
                     END
   WHERE user_name IN ( 'Bob', 'John' )

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