sql-server - 如何重用计算列避免重复sql语句

Question

我有很多计算列，它们不断重复自己，一个在其他列里面，包括嵌套的 case 语句。

有一个非常简化的版本，我一直在寻找一种方法来做。

SELECT 
    (1+2) AS A, 
    A + 3 AS B, 
    B * 7 AS C 
FROM MYTABLE

Answer 1

你可以尝试这样的事情。

SELECT 
    A.Val AS A, 
    B.Val AS B, 
    C.Val AS C 
FROM MYTABLE
  cross apply(select 1 + 2) as A(Val)
  cross apply(select A.Val + 3) as B(Val)
  cross apply(select B.Val * 7) as C(Val)