比较 2 列，然后对 MySQL 中的另一列执行操作 [英] Compare 2 columns, then perform action on another column in MySQL

问题描述

我在 MySQL 中有一个名为 TableX 的表.TableX 中有 4 列.列是 ColumnCompare_Now、ColumnCompare_Past、ColumnNumber_Now、ColumnNumber_Past.

I have a table named TableX in MySQL. There are 4 columns in TableX. The columns are ColumnCompare_Now, ColumnCompare_Past, ColumnNumber_Now, ColumnNumber_Past.

我想写一个具有如下逻辑的MySQL语句；

I want to write a MySQL statement that has the following logic;

    If ColumnCompare_Now == 'ActionNeeded' and ColumnCompare_Past == 'ActionNeeded', 
          then ColumnNumber_Now = `ColumnNumber_Now` + `ColumnNumber_Past`

MySQL 知识仅限于简单的 Select Where 语句.以上操作如何在MySQL中实现?同时，我会在等待 StackOverflow 其他成员的帮助的同时尝试自己解决这个问题.

MySQL knowledge is limited to simple Select Where statements. How can the above operation be implemented in MySQL? Meanwhile, I will try to figure this out myself while waiting for help from fellow members of StackOverflow.

推荐答案

我不完全确定我知道你想要完成什么.如果要选择包含此信息的新列，可以使用 case 语句:

I'm not completely sure I know what you're trying to accomplish. If you want to select a new column with this information, you can use a case statement:

select 
    case when ColumnCompare_Now = 'ActionNeeded' 
              and ColumnCompare_Past = 'ActionNeeded'
         then ColumnNumber_Now + ColumnNumber_Past
         else ColumnNumber_Now
    end as ColumnNumber_Now 
from tablex

<小时>

如果你在 update 查询中需要这个:

update tablex
set ColumnNumber_Now = ColumnNumber_Now + ColumnNumber_Past
where ColumnCompare_Now = 'ActionNeeded' 
    and ColumnCompare_Past = 'ActionNeeded'

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