如何根据其他两列的算术创建临时列？

Question

我想要实现以下目标：

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

Answer 1

你的语法还不远，试试这个：

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

列别名的通用ANSI语法是：

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

Answer 2

从some_table选择a，b，a-b作为差异;