SQL-即使项目的计数为零，也返回所有行

Question

我正在根据日期范围进行计数。当前查询确实返回正确的结果，但我需要其他信息。在当前形式下，查询将显示具有正确计数的项目。但是，我需要显示所有项目，即使在指定的日期范围内它们的计数为零。

这是SQL代码：

INSERT INTO @CreationCount (BaselineID, Name)

SELECT distinct [BaselineID],[Name] 
FROM [Baseline_INFO]

DECLARE @ReqType TABLE (Type nvarchar(128))
INSERT INTO @ReqType (Type)
SELECT DISTINCT Tree.Type as 'Requirement Type'
FROM [TREE]
INNER JOIN [Project_INFO]  ON [Project_INFO].[ProjectID]=[Tree].[Project_ID] 
INNER JOIN [Baseline_INFO] ON [Baseline_INFO].[BaselineID]=[Tree].[Baseline_ID]
WHERE [Project_INFO].[Name] = 'Address Book' AND [Baseline_INFO].[Name] = 'Current
Baseline' 
Group By Tree.Type

SELECT Tree.Type as 'Requirement Type', COUNT(Tree.Type) as 'Number in Creation Range' 
FROM [Tree] 
INNER JOIN @ReqType As RT on RT.Type = Tree.Type
INNER JOIN [Project_INFO]  ON [Project_INFO].[ProjectID]=[Tree].[Project_ID] 
INNER JOIN @CreationCount AS CCount ON CCount.BaselineID=Tree.Baseline_ID 
WHERE [Project_INFO].[Name] = 'Address Book' AND CCount.Name = 'Current Baseline' 
AND [Tree].[creationDate] >= ('2010-01-01') and [Tree].[creationDate] < ('2020-01-01') 
GROUP BY tree.Type

当我执行此查询时，我得到以下结果：

https://dl.dropbox.com/u/17234826/SQLresult.png

这个结果是正确的，但是即使创建范围中没有需求，我也需要列出所有需求类型，即

https://dl.dropbox.com/u/17234826/SQLresult1.png

我尝试使用各种联接，IFNULL和ISNULL，但没有任何工作。

如果有人能指出我正确的方向，我将不胜感激。

Answer 1

修改第二个查询

SELECT Tree.Type as 'Requirement Type',
       COUNT(CASE WHEN [Tree].[creationDate] >= ('2010-01-01') and [Tree].[creationDate] < ('2020-01-01') THEN Tree.Type END) AS 'Number in Creation Range'
FROM [Tree] 
INNER JOIN @ReqType As RT on RT.Type = Tree.Type
INNER JOIN [Project_INFO]  ON [Project_INFO].[ProjectID]=[Tree].[Project_ID] 
INNER JOIN @CreationCount AS CCount ON CCount.BaselineID=Tree.Baseline_ID 
WHERE [Project_INFO].[Name] = 'Address Book' AND CCount.Name = 'Current Baseline' 
GROUP BY tree.Type