存儲子查詢結果作爲列別名重用

Question

我想創建一個包含計數的列，但問題是我重新使用子查詢的位置，因爲它以前創建的臨時表變得不可用，因爲它不再存在。

我的問題是我如何存儲以前的子查詢的結果，所以我可以稍後在同一個查詢中運行一些結果？

首先用於計數我有：

CREATE TEMPORARY TABLE _temp_unique_entity_manufacturers 
      (
       entityId INT(11), 
       manufacturerRef INT(11), 
       manufacturerName VARCHAR(255), 
       KEY(entityId), 
       KEY(manufacturerRef) 
      ) 
      ENGINE=MEMORY AS 
       (SELECT DISTINCT entityRef AS entityId, manufacturer AS manufacturerRef, pm.name AS manufacturerName FROM enquiries, parts_trading, parts_manufacturers AS pm WHERE manufacturer = pm.id AND enquiryRef = enquiries.id) 

然後在我的主查詢我這個表的工作，特別是這部分：

IF((SELECT COUNT(*) FROM _temp_unique_entity_manufacturers WHERE entityId = eo.id) > 0, 
    (SELECT COUNT(*) FROM _temp_unique_entity_manufacturers WHERE entityId = eo.id), 
    0 
) AS manufacturers 

第二子查詢失敗，因爲臨時表是在這一點上走了。有沒有一種方法，我不必一次又一次寫出相同的子查詢？

Answer 1

 case when 
     ((SELECT COUNT(*) FROM _temp_unique_entity_manufacturers WHERE entityId = eo.id) > 0) then 
      (SELECT COUNT(*) FROM _temp_unique_entity_manufacturers WHERE entityId = eo.id) else 
      0 end 
     ) AS manufacturers 
    -------------- 
    ex: 
    select coname,(case when cond then result else second result end) as user_colname from 
    tablename 
---------------------- 
If condition implement in sql as case when statement