在SQL中添加一个临时列，其中值取决于另一列 [英] add a temporary column in SQL, where the values depend from another column

问题描述

我有这张桌子:

ID | name | result | 
--------------------    
 1 |  A   |   1    |
--------------------
 2 |  B   |   2    |
--------------------
 3 |  C   |   1    |
--------------------
 1 |  A   |   2    |
--------------------
 4 |  E   |   2    |
--------------------

我想在| result |旁边添加一个新的临时列，其中result = 1的值应为100，而result = 2的值应为80，因此应如下所示:

I want to add a new temporary column next to |result|, and where result=1 the value should be 100, and where result=2 the value should be 80 so it should look like this:

ID | name | result | NewColumn|
-------------------------------    
 1 |  A   |   1    |  100     |
-------------------------------
 2 |  B   |   2    |   80     |
-------------------------------
 3 |  C   |   1    |  100     |
-------------------------------
 1 |  A   |   2    |  80      |
-------------------------------
 4 |  E   |   2    |  80      |
-------------------------------

如何在SQL中查询呢?

How can I query this in SQL ?

推荐答案

使用 SELECT的列列表中的CASE表达式-像这样:

Use a CASE expression in your SELECT's column list - something like this:

SELECT
    ID,
    name,
    result,
    CASE
        WHEN result = 1 THEN 100
        WHEN result = 2 THEN 80
        ELSE NULL
    END AS NewColumn
FROM YourTable

根据需要添加其他WHEN表达式或更改ELSE表达式.

Add additional WHEN expressions or alter the ELSE expression as needed.

这篇关于在SQL中添加一个临时列，其中值取决于另一列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！