警告：在Aqua Data Studio中通过聚合或其他SET操作消除了空值

当数据为空并且显示结果时出现警告，我遇到了问题。如何解决这个问题呢？。当表中没有数据时，如何将空数据更改为0？

这是我的代码：

SELECT DISTINCT c.username             AS assigner_officer,
                d.description          AS ticketcategory,
                (SELECT Count(closed)
                 FROM   ticket
                 WHERE  assigned_to = c.user_id
                        AND closed IS NOT NULL
                 GROUP  BY assigned_to)closedcases,
                (SELECT Count(closed)
                 FROM   ticket
                 WHERE  assigned_to = c.user_id
                        AND closed IS NULL
                 GROUP  BY assigned_to)opencases
FROM   ticket a
       JOIN ticketlog b
         ON a.ticketid = b.ticketid
       JOIN access c
         ON a.assigned_to = c.user_id
       JOIN ticket_category d
         ON a.cat_code = d.id
       JOIN lookup_department e
         ON a.department_code = e.code 

结果显示如下：

 Warnings: ---> 
   W (1): Warning: Null value is eliminated by an aggregate or other SET operation.
          <--- 
 assigner_officer     ticketcategory     closedcases     opencases    
 -------------------  -----------------  --------------  ------------ 
 abdulhafiz           Enquiry            (null)          0            
 affan                Enquiry            12              (null)       
 amirul               Enquiry            1               (null)       
 azrul_fahmi          Enquiry            45              0            
 Azwani               Enquiry            (null)          0            
 chai                 Enquiry            4               (null)       
 dalinawati           Enquiry            1               0            
 Emmy                 Complaints         (null)          0            
 Fadhlia              Enquiry            38              0            
 fairulhalif          Others             1               (null)       
 farikh               Enquiry            (null)          0            
 ismailh              Enquiry            28              0            
 izzahanna            Enquiry            (null)          0            
 Kamsuzilawati        Enquiry            1               (null)     

您通常会使用COUNTUID进行汇总。因此

COUNT([uid]) 将产生警告：

警告：通过合计或其他SET操作消除了空值。

与左联接一起使用时，其中不存在被计数的对象。

COUNT(*)在这种情况下使用也会导致不正确的结果，因为您将要计算存在的结果总数（即父母）。

使用COUNT([uid])IS是一种有效的计数方式，而警告仅是警告。但是，如果您担心这种情况下想要获得真正的uid计数，则可以使用：

SUM(CASE WHEN [uid] IS NULL THEN 0 ELSE 1 END) AS [new_count]

这不会为您的查询增加很多开销。（已测试mssql 2008）

解决此问题的一种方法是关闭警告。

SET ANSI_WARNINGS OFF;
GO

用途ISNULL(field, 0)还可以与聚集体一起使用：

ISNULL(count(field), 0)

但是，您可以考虑更改 count(field) to count(*)

编辑：

尝试：

closedcases = ISNULL(
   (select count(closed) from ticket       
    where assigned_to = c.user_id and closed is not null       
    group by assigned_to), 0), 

opencases = ISNULL(
    (select count(closed) from ticket 
     where assigned_to = c.user_id and closed is null 
     group by assigned_to), 0),

您想将函数放在ISNULL内部COUNT，而不是外部：

不好： ISNULL(COUNT(field), 0)

好： COUNT(ISNULL(field, 0))

我收到此错误；我只是WHERE为在子句中使用的字段添加了一个count子句。它解决了这个问题。注意：如果存在空值，请检查其是否对报告至关重要，因为计数中未包括该值。

旧查询：

select city, Count(Emp_ID) as Emp_Count 
from Emp_DB
group by city

新查询：

select city, Count(Emp_ID) as Emp_Count 
from Emp_DB
where Emp_ID is not null
group by city

如果聚合函数中存在任何Null值，您将面临此问题。代替下面的代码

 SELECT Count(closed)
  FROM   ticket
  WHERE  assigned_to = c.user_id
  AND closed IS NULL

使用像

SELECT Count(ISNULL(closed, 0))
  FROM   ticket
  WHERE  assigned_to = c.user_id
  AND closed IS NULL