如何根据其他两列的算术结果创建一个临时列？

Question

我想实现以下目标：

select a, 
       b,
       diff as (b-a)
from some_table;

Answer 1

你的语法并不遥远，试试这个：

select a, 
       b,
       b - a as diff
from some_table;

为列添加别名的通用 ANSI 语法是：

select <expression involving columns> as <alias name>
from some_table

Answer 2

选择 a,b,a-b 作为与 some_table 的差异；