如果连接的表中缺少记录，则返回SQL中的NULL

Question

早上好。我一直在努力解决这个问题一段时间了，我似乎无法围绕它解决问题。

所以我在数据库的两个表

tblDateTrans 

CREATE TABLE [dbo].[tblDateTrans](
    [Date] [smalldatetime] NOT NULL, 
) 

此表是包含1/1/2007的所有日期的外部日历表 - 1/1/2011，它也包含像addtional信息假期信息，公司期间等。但这对于这个问题并不重要。

我的第二个表是

tblSurveySession 
    CREATE TABLE [dbo].[tblSurveySession](
     [surveySessionID] [int] IDENTITY(1,1) NOT NULL, 
     [guestID] [int] NULL, 
     [surveyID] [int] NOT NULL, 
     [FK_StoreId] [int] NULL, 
     [surveyCompletedDate] [datetime] NULL 
) 

此表包含在一段时间内送出，并通过我们的客人完成的调查名单。 FK_StoreId是公司的业务单位ID，surveyCompletedDate只包含日期而不包含任何时间。

我的目标是使用tblDateTrans表上的LEFT OUTER JOIN返回surveySessionIDs和日期的列表，我想返回所有日期，无论是否有值。于是，我就运行此查询：

SELECT  tblDateTrans.Date, dbo.tblSurveySession.surveySessionID, dbo.tblSurveySession.FK_StoreId 
FROM   OPENQUERY([APOLLO], 'select Date FROM apollo.nhcglobal.dbo.tblDateTrans') AS tblDateTrans LEFT OUTER JOIN 
         dbo.tblSurveySession ON tblDateTrans.Date = dbo.tblSurveySession.surveyCompletedDate 
WHERE  (tblDateTrans.Date >= '1/1/2010') AND (tblDateTrans.Date <= '2/1/2010') AND (dbo.tblSurveySession.FK_StoreId = 4) 

我返回的数据看起来像这样：

Date     surveySessionID  FK_StoreId 
2010-01-01 00:00:00.000  12702   4 
2010-01-01 00:00:00.000  12736   4 
2010-01-01 00:00:00.000  12456   4 
2010-01-03 00:00:00.000  12662   4 
2010-01-04 00:00:00.000  12660   4 
2010-01-05 00:00:00.000  12510   4 
2010-01-05 00:00:00.000  12889   4 
2010-01-24 00:00:00.000  13751   4 
2010-01-25 00:00:00.000  13793   4 
2010-01-28 00:00:00.000  13958   4 
2010-01-30 00:00:00.000  14059   4 
2010-01-31 00:00:00.000  14139   4 

我的目标就是让查询返回像这样的数据：

Date     surveySessionID  FK_StoreId 
2010-01-01 00:00:00.000  12702   4 
2010-01-01 00:00:00.000  12736   4 
2010-01-01 00:00:00.000  12456   4 
2010-01-02 00:00:00.000  NULL   NULL 
2010-01-03 00:00:00.000  12662   4 
2010-01-04 00:00:00.000  12660   4 
2010-01-05 00:00:00.000  12510   4 
2010-01-05 00:00:00.000  12889   4 
2010-01-06 00:00:00.000  NULL   NULL 
2010-01-07 00:00:00.000  NULL   NULL 
2010-01-08 00:00:00.000  NULL   NULL 
2010-01-09 00:00:00.000  NULL   NULL 
2010-01-10 00:00:00.000  NULL   NULL 
2010-01-11 00:00:00.000  NULL   NULL 
2010-01-12 00:00:00.000  NULL   NULL 
2010-01-13 00:00:00.000  NULL   NULL 
2010-01-14 00:00:00.000  NULL   NULL 
2010-01-15 00:00:00.000  NULL   NULL 
2010-01-16 00:00:00.000  NULL   NULL 
2010-01-17 00:00:00.000  NULL   NULL 
2010-01-18 00:00:00.000  NULL   NULL 
2010-01-19 00:00:00.000  NULL   NULL 
2010-01-20 00:00:00.000  NULL   NULL 
2010-01-21 00:00:00.000  NULL   NULL 
2010-01-22 00:00:00.000  NULL   NULL 
2010-01-23 00:00:00.000  NULL   NULL 
2010-01-24 00:00:00.000  13751   4 
2010-01-25 00:00:00.000  13793   4 
2010-01-28 00:00:00.000  13958   4 
2010-01-30 00:00:00.000  14059   4 
2010-01-31 00:00:00.000  14139   4 

我计算出LEFT OUTER JOIN会强制查询查看所有日期并在缺少surveySessionIDs和FK_StoreIds的日子返回NULLS。我们之前遇到过这样的问题，因此解决这个问题对我们来说是一个巨大的帮助。谢谢大家的帮助！

Answer 1

移动从哪里来的离开了(dbo.tblSurveySession.FK_StoreId = 4) JOIN的ON条款，如：

LEFT OUTER JOIN dbo.tblSurveySession ON tblDateTrans.Date = dbo.tblSurveySession.surveyCompletedDate AND dbo.tblSurveySession.FK_StoreId = 4 

Answer 2

由于您的WHERE子句，您正在过滤掉一些所需的行。尝试从此改变你的WHERE子句中，也允许空值，即最后一部分：

AND (dbo.tblSurveySession.FK_StoreId = 4) 

这样：

AND (dbo.tblSurveySession.FK_StoreId = 4 OR 
    dbo.tblSurveySession.FK_StoreId IS NULL) 

Answer 3

反转的连接方向

SELECT tblDateTrans.Date, dbo.tblSurveySession.surveySessionID, dbo.tblSurveySession.FK_StoreId 
FROM OPENQUERY([APOLLO], 'select Date FROM apollo.nhcglobal.dbo.tblDateTrans') AS tblDateTrans 
LEFT OUTER JOIN dbo.tblSurveySession 
    ON tblDateTrans.Date = dbo.tblSurveySession.surveyCompletedDate 
    AND (dbo.tblSurveySession.FK_StoreId = 4) 
WHERE (tblDateTrans.Date >= '1/1/2010') AND (tblDateTrans.Date <= '2/1/2010')