如何在同一视图中使用计算列来计算另一列 [英] How to use a calculated column to calculate another column in the same view

问题描述

我希望您能为这个问题提供帮助.我正在使用Oracle SQL(此视图为SQL Developer)...

I am hoping you can help with this question. I am using Oracle SQL (SQL Developer for this view)...

如果我有一个包含以下列的表格:

If I have a table with the following columns:

• ColumnA(数字)
• ColumnB(数字)
• ColumnC(数字)

我认为

Select  
ColumnA,
ColumnB,
ColumnA + ColumnB As calccolumn1

现在，我要使用calccolumn1 但我不能只说...

Now at this point, I want to use calccolumn1 but I cannot just say...

Select  
ColumnA,
ColumnB,
ColumnA + ColumnB As calccolumn1
calccolumn1 / ColumnC as calccolumn2

我假设我需要某种子查询..但这是我需要您帮助的地方... 我将如何用词查询查询，以便可以在同一查询的另一个计算中使用calccolumn1?可能是"If then"或"Case when"，但最重要的是它是一些派生数字.

I am assuming I need some type of subquery..but this is where I need your help... How would I word the query so that I can use calccolumn1 in another calculation within the same query? It might be an If then or a Case when, but bottomline it is some derived number.

推荐答案

您可以使用嵌套查询:

Select
  ColumnA,
  ColumnB,
  calccolumn1,
  calccolumn1 / ColumnC as calccolumn2
From (
  Select
    ColumnA,
    ColumnB,
    ColumnC,
    ColumnA + ColumnB As calccolumn1
  from t42
);

具有值3，4，5的行给出:

   COLUMNA    COLUMNB CALCCOLUMN1 CALCCOLUMN2
---------- ---------- ----------- -----------
         3          4           7         1.4

您也可以重复第一个计算，除非它确实在做一些昂贵的事情(例如通过函数调用):

You can also just repeat the first calculation, unless it's really doing something expensive (via a function call, say):

Select
  ColumnA,
  ColumnB,
  ColumnA + ColumnB As calccolumn1,
  (ColumnA + ColumnB) / ColumnC As calccolumn2
from t42; 

   COLUMNA    COLUMNB CALCCOLUMN1 CALCCOLUMN2
---------- ---------- ----------- -----------
         3          4           7         1.4 

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