Question

我确定这是因为我不知道如何使用LEFT JOIN，但我正在编写一个不返回NULL值的查询。这是查询：

CREATE TABLE #OrgMaster
(OrgName nvarchar(100))

INSERT INTO #OrgMaster (OrgName)
SELECT DISTINCT Organization
FROM StageReleaseCalendar_VW

SELECT SRC.Organization
, SRC.deploytype
, COUNT(SRC.deploytype) AS 'Deployment Count'
, DATEPART(m,SRC.actualstarttime) AS 'MonthNum'
, DATENAME(m,SRC.actualstarttime) AS 'MonthNam'
 FROM #OrgMaster TTOM LEFT OUTER JOIN StageReleaseCalendar_VW SRC 
 ON LEFT(TTOM.OrgName, LEN(TTOM.OrgName)) = SRC.Organization
WHERE DATEDIFF(m, SRC.scheduledstarttime, CURRENT_TIMESTAMP) BETWEEN 1 AND 2
AND completerelease = 1
AND deploytype IN ('Service Pack','Hot Fix')
AND cancelled = 0
GROUP BY SRC.Organization, SRC.deploytype,  DATEPART(m,SRC.actualstarttime), DATENAME(m,SRC.actualstarttime)

DROP TABLE #OrgMaster

总共有四个组织：商业，消费者，合作伙伴和销售。创建临时表后，如果我然后运行以下查询：

SELECT OrgName FROM #OrgMaster

结果如下：

商业消费者伙伴销售

合作伙伴在7月或8月没有任何类型的部署，所以我想要得到的是一组结果，包括合作伙伴的四个NULL记录 - 七月份的修补程序记录，八月份的修补程序，用于服务7月打包，8月打包服务。相反，我得到的结果集仅限于部署实际发生的那些条目。

有人能看到我在这里不理解的东西吗？

感谢。

Answer 1

问题是你的where子句按（右）表中的字段限制数据。这不会给你空值。为此，我经常将SELECT包含在另一个SELECT（嵌套）中，这样我就可以在（右）表中查询空值。

SELECT * FROM (
SELECT a.ID as AID, b.ID as BID from TableA a
LEFT JOIN TableB b
On ....
WHERE ...
) tmp Where BID is null

Answer 2

正确的查询

SELECT TTOM.OrgName 
, SRC.deploytype
, COUNT(SRC.deploytype) AS 'Deployment Count'
, DATEPART(m,SRC.actualstarttime) AS 'MonthNum'
, DATENAME(m,SRC.actualstarttime) AS 'MonthNam'
 FROM #OrgMaster TTOM LEFT OUTER JOIN StageReleaseCalendar_VW SRC 
 ON LEFT(TTOM.OrgName, LEN(TTOM.OrgName)) = SRC.Organization
WHERE SRC.Organization is null or 
 DATEDIFF(m, SRC.scheduledstarttime, CURRENT_TIMESTAMP) BETWEEN 1 AND 2
AND deploytype IN ('Service Pack','Hot Fix')
AND completerelease = 1
AND cancelled = 0
GROUP BY TTOM.OrgName, SRC.deploytype,  DATEPART(m,SRC.actualstarttime), DATENAME(m,SRC.actualstarttime)

另一种选择是使用ISNULL运算符保护WHERE子句中SCR表的所有字段。

Answer 3

这对你有用。另外，我认为您也可以使用它来获取其他好的信息。

DECLARE @OrgMaster as table(OrgName nvarchar(100),deptype nvarchar(100),MonthNum int,DeploymentCount int)
DECLARE @Loop1 int
DECLARE @Loop2 int

SELECT @Loop1 = 0, @Loop2 = 0

WHILE @Loop1 <> 2
BEGIN
    SELECT @Loop1 = @Loop1 + 1, @Loop2 = 0

    WHILE @Loop2 <> 2
    BEGIN
        SET @Loop2 = @loop2 + 1

        INSERT INTO @OrgMaster (OrgName,deptype,MonthNum)
        SELECT DISTINCT 
            Organization
            ,CASE WHEN @Loop1 = 1 THEN 'Service Pack' ELSE 'Hot Fix' END
            ,DATEPART(m,DATEADD(MONTH, -1 * @Loop2, GETDATE()))
        FROM StageReleaseCalendar_VW

    END
END


UPDATE @OrgMaster SET
    DeploymentCount = (SELECT COUNT(*) 
                        FROM StageReleaseCalendar_VW 
                        WHERE Organization = OrgName
                            AND deploytype = deptype
                            AND DATEPART(m,actualstarttime) = MonthNum
                            )

SELECT * from @OrgMaster where DeploymentCount = 0

left join不返回NULL值

3 个答案: