mysql - 即使条件为真，我的sql Select IF也会返回else结果

Question

该请求返回Else结果即使条件为真，也会显示“ELSE RESULT”。

SELECT
   IF(Print_Server_Type='BW',SUM(Total_Impressions_Printed),'ELSE RESULT') AS BWTotalImpressions
FROM printedjob
WHERE
  Account=''
  And Job_Submission_Date>="2015-08-24"
  AND Job_Submission_Date<="2015-08-28"; 

与 where 条件相同的请求可以正常工作

SELECT
  SUM(Total_Impressions_Printed) AS BWTotalImpressions
FROM printedjob
WHERE
  Account=''
  And Print_Server_Type='BW'
  And Job_Submission_Date>="2015-08-24"
  AND Job_Submission_Date<="2015-08-28"; 

我使用第一个请求，因为我需要结果是选择中的一列。

Answer 1

您正在混合聚合术语(例如 SUM(Total_Impressions_Printed))和单行术语(例如 Print_Server_Type)。似乎您正在尝试针对 Print_Server_Type 的每个值返回一行，这意味着您缺少 group by 子句:

SELECT   Print_Server_Type, 
         IF(Print_Server_Type = 'BW',
            SUM(Total_Impressions_Printed), 
            'ELSE RESULT') AS BWTotalImpressions
FROM     printedjob
WHERE    Account = '' AND 
         Job_Submission_Date >= "2015-08-24" AND 
         Job_Submission_Date <= "2015-08-28"
GROUP BY Print_Server_Type