SQL Group by Max Date Including Null

Question

下面的代码用相同的项目名称和不同的日期对多个记录进行分组。

问题是日期字段中的某些日期为空。我需要这种代码的方式来包含最大日期或空值。

我尝试添加或受日期为空，但那时，只是让我回到我的问题与具有多个记录

原始SQL

SELECT t1.Project_Name, t1.IssueNmb, t1.Date 
FROM Milestones_Detail_Report_Table AS t1 
WHERE (((t1.Date)=(SELECT Max(t2.Date) 
    FROM Table_Name t2 
    WHERE t2.Project_Name=t1.Project_Name 
    GROUP BY t2.Project_Name))) 

SQL与OR

SELECT t1.Project_Name, t1.IssueNmb, t1.Date 
FROM Milestones_Detail_Report_Table AS t1 
WHERE (((t1.Date)=(SELECT Max(t2.Date) 
    FROM Table_Name t2 
    WHERE t2.Project_Name=t1.Project_Name 
    GROUP BY t2.Project_Name))) OR (((t1.Date) Is Null)); 

项目表：表名

Project_Name | IssueNmb | Date 
------------------------ 
    Car  | 1  | 1/1/15 
    Car  | 1  | 2/1/15 <--This record populates 
    House  | 1  |  <--This record does NOT populate 

Answer 1

你可能想这where条款：

WHERE (t1.Date IS NULL) OR 
     (t1.Date = (SELECT iif(COUNT(*) <> COUNT(t2.Date), NULL, Max(t2.Date)) 
        FROM Table_Name t2 
        WHERE t2.Project_Name = t1.Project_Name 
       ) 
    ) 

这将把NULL的最大日期，所以会出现在子查询没有匹配如果t2.Date任何值NULL给定项目。

请注意，子查询中不需要group by。