Oracle:在同一Select语句中使用伪列值 [英] Oracle: Using Pseudo column value in the same Select statement

问题描述

我在oracle中有一个场景，我需要能够重用先前在同一select语句中计算出的伪列的值，例如:

I have a scenario in oracle where i need to be able to reuse the value of a pseudo column which was calculated previously within the same select statement something like:

select 'output1' process, process || '-Output2' from Table1

出于维护目的，我不想在第二列中再次重复第一列逻辑，

I don't want to the repeat the first columns logic again in the second column for maintenance purposes, currently it is done as

select 'output1' process, 'output1' || '-Output2' name from Table1

由于我有4个这样的列，具体取决于上一列的输出，因此重复将是维护的噩梦

since i have 4 such columns which depend on the previous column output, repeating would be a maintenance nightmare

我添加了表名并删除了对偶表，因此没有任何关于这不是一个复杂过程的假设，我的实际语句在不同的表上确实有2到3个连接

i included table name and removed dual, so that no assumptions are made about that this is not a complex process, my actual statement does have 2 to 3 joins on different tables

推荐答案

您可以在子查询中计算值:

You could calculate the value in a sub-query:

select calculated_output process, calculated_output || '-Output2' name from
(
    select 'output1' calculated_output from dual
)

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