如何基于另一个列的值在SQL选择查询中创建/添加列? [英] How to create/add a column in an SQL select query based on another column's values?

问题描述

我想根据条件通过SQL选择查询动态添加另一列hook_name.

I want to dynamically add another column hook_name, via an SQL select query, based on a condition.

例如，如果hook_type = 0，表hook_name的值应为OFFER，并且对于hook_type = 1，hook_name的值应显示为"ACCEPT".

For example if hook_type = 0, table hook_name should have a value of OFFER, and similarly for hook_type = 1, hook_name should show "ACCEPT".

下面是结果的屏幕截图:

Below is a screenshot of the result:

选择查询是这样的:

select hook_type, 'hook name' as hook_name,
       count(*) as number_of_exchange_activities 
from `exchange` 
group by hook_type # hook_type 0 for OFFER, 1 for ACCEPT and 2 for offer EXPIRED;

提前谢谢.

推荐答案

使用标准的SQL CASE:

Use a Standard SQL CASE:

SELECT hook_type, 
   CASE hook_type
      WHEN 0 THEN 'OFFER'
      WHEN 1 THEN 'ACCEPT'
      WHEN 2 THEN 'EXPIRED'
   END AS hook_name,
   COUNT(*) AS number_of_exchange_activities 
FROM `exchange` 
GROUP BY hook_type

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