如何創建一個臨時列作爲其他兩列的算術結果？

Question

我想acheive如下：

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

Answer 1

你的語法已經不遠了，試試這個：

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

混疊列的一般ANSI語法是：

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

Answer 2

從some_table中選擇a，b，ab作爲diff;