如何根據另一列的值在SQL select查詢中創建/添加列？

Question

我想根據條件通過SQL select查詢動態添加另一個列hook_name 。

例如，如果hook_type = 0 ，則表hook_name的值應為OFFER ，類似於hook_type = 1 ， hook_name應顯示“ACCEPT”。

以下是結果的屏幕截圖：

選擇查詢是這樣的：

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;

提前致謝。

Answer 1

使用標准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

Answer 2

select case when hook_type = 0 then 'offer'
            when hook_type = 1 then 'accept'
            else 'expired'
       end as hook_t, 
      `hook name` as hook_name,
      count(*) as number_of_exchange_activities 
from `exchange` 
group by hook_t

BTW我想你想要轉義列名hook name 。 然后使用反引號而不是引號。