PostgreSQL视图：在另一个计算字段中引用一个计算字段

本文介绍了PostgreSQL视图：在另一个计算字段中引用一个计算字段的处理方法，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

我与＃1895500 ，但使用PostgreSQL而不是MySQL。

I have the same question as #1895500, but with PostgreSQL not MySQL.

如何定义具有计算字段的视图，例如：

How can I define a view that has a calculated field, for example:

(mytable.col1 * 2) AS times_two

...并创建基于第一个字段的另一个计算字段：

... and create another calculated field that's based on the first one:

(times_two * 2) AS times_four

...？

推荐答案

根据formla的沉重程度，您可以使用子查询：

Depending on how heavy the formla is, you could use a subquery:

select inner.*, times_two * 2 from (select mycol * 2 as times_two from table) sub

或重写计算：

select mycol * 2, mycol * 2 * 2 from table