如何创建一个临时列作为其他两列的算术结果？

Question

我想acheive如下：

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

Answer 1

你的语法已经不远了，试试这个：

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

混叠列的一般ANSI语法是：

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

Answer 2

从some_table中选择a，b，ab作为diff;