left join not returning NULL values

Question

I'm sure this is due to the fact that I don't know how to use LEFT JOIN, but I'm writing a query that is not returning NULL values. Here's the query:

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

There are four organizations total: Commercial, Consumer, Partner, and Sales. After creating the temp table, if I then run the following query:

SELECT OrgName FROM #OrgMaster

The results are as follows:

Commercial Consumer Partner Sales

Partner has no deployments of any kind in July or August, so what I'm trying to get is a set of results that includes four NULL records for Partner - a record for hotfixes in July, for hotfixes in August, for service packs in July, and for service packs in August. Instead, I get a result set that is limited to only those entries for which a deployment did in fact take place.

Can anyone see what I'm not understanding here?

Thanks.

Answer 1

The problem is your where clause limits data by fields in your (right) table. This will not give you the nulls. To do this, I often encase my SELECT inside another SELECT (nested), so I can then query for nulls in the (right) table.

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

The proper query

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)

Another option would be to guard all the fields from SCR table in WHERE clause with ISNULL operator.

Answer 3

This will work for you. Plus, I think you can use this to get other good information as well.

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