如何在不向SQL中的表添加新列的情况下使用CASE

Question

如何根据条件更改CASE命令的列值而不向表中添加新列？

我知道的唯一方法是添加新列：

SELECT 
    t1.*
    ,CASE
        what='costs' THEN amount*(-1)
    ELSE
    sales
    END AS NewAmount
FROM t1

有没有办法得到如下图所示的结果？请注意，有时条件由多个列中的值指定（what = costs AND country = Atlantida）

Answer 1

只选择您想要的列：

SELECT t1.what, 
       (CASE WHEN what = 'costs' THEN amount*(-1)
             ELSE sales
        END) AS Amount
FROM t1

Answer 2

是的，有办法， 而不是select *，而只使用必需的列名。

SELECT 
    t1.what
    ,CASE
        WHEN what='costs' THEN amount*(-1)
    ELSE
    sales
    END AS Amount
FROM t1

Answer 3

不花费金额？

SELECT 
    t1.*
    ,CASE when what='costs' THEN amount*(-1)
     ELSE
        amount
     END AS NewAmount
FROM t1