Showing all values in Group By with inclusion of CASE - sql

Question

I have the following data
CREATE TABLE #Test
(
Severity NVARCHAR(50)
,WorkId INT
)
INSERT INTO #Test VALUES('High',1)
INSERT INTO #Test VALUES('Critical',2)
SELECT
CASE
WHEN Severity IN ('High','Critical') THEN 'Critical'
WHEN Severity IN ('Low','Medium') THEN 'Medium'
END AS 'Severity'
,COUNT(*) AS 'Total'
FROM #Test
GROUP BY
CASE
WHEN Severity IN ('High','Critical') THEN 'Critical'
WHEN Severity IN ('Low','Medium') THEN 'Medium'
END
This results in output -
Severity | Total
---------+-------
Critical | 2
I am expecting the following output -
Severity | Total
---------+-------
Critical | 2
Medium | 0
I have looked into the following two links which details a similar case but not same and am still unable to get the result -
http://ask.sqlservercentral.com/questions/47705/showing-null-values-as-well-in-group-by-in-sql.html
How to return empty groups in SQL GROUP BY clause
Any help or links?
Further update.
Having tried the solution below, the results are still not appearing. Pasting here the actual code wherein I would need to apply the logic
SELECT s.NewSeverity AS 'Severity'
,COUNT(WI.microsoft_vsts_common_severity) AS 'Total'
FROM ( VALUES
('Critical','I-High')
,('High','I-High')
,('Medium','I-Low')
,('Low','I-Low')
)s(OldSeverity,NewSeverity)
LEFT JOIN DimWorkItem WI (NOLOCK)
ON WI.microsoft_vsts_common_severity = s.OldSeverity
JOIN dbo.DimPerson P
ON p.personsk = WI.system_assignedto__personsk
JOIN DimTeamProject TP
ON WI.TeamProjectSK = TP.ProjectNodeSK
JOIN DimIteration Itr (NOLOCK)
ON Itr.IterationSK = WI.IterationSK
JOIN DimArea Ar (NOLOCK)
ON Ar.AreaSK = WI.AreaSK
WHERE TP.ProjectNodeName = 'ABC'
AND WI.System_WorkItemType = 'Bug'
AND WI.Microsoft_VSTS_CMMI_RootCause <> 'Change Request'
AND Itr.IterationPath LIKE '%\ABC\R1234\Test\IT%'
AND WI.System_State NOT IN ( 'Rejected', 'Closed' )
AND WI.System_RevisedDate = CONVERT(datetime, '9999', 126)
GROUP BY s.NewSeverity
In actual there are only two 'Low' items, hence the output I am getting is I-Low, 2 whereas I want even I-High to appear with 0 count.

Answer 1

The way I would go about this is to create your own table of values using a table value constructor:
SELECT OldSeverity, NewSeverity
FROM (VALUES
('Critical', 'Critical'),
('High', 'Critical'),
('Medium', 'Medium'),
('Low', 'Medium')
) s (OldSeverity, NewSeverity);
This gives a table you can select from, then left join to your existing table:
SELECT Severity = s.NewSeverity,
Total = COUNT(t.Severity)
FROM (VALUES
('Critical', 'Critical'),
('High', 'Critical'),
('Medium', 'Medium'),
('Low', 'Medium')
) s (OldSeverity, NewSeverity)
LEFT JOIN #Test t
ON t.Severity = s.OldSeverity
GROUP BY s.NewSeverity;
This will give the desired results.
Example on SQL Fiddle
EDIT
The problem you have with the way that you are implimenting the query, is that although you have immediately left joined to DimWorkItem you then inner join to subsequent tables and refer to columns in WorkItem in the where clause, which undoes your left join and turns it back into an inner join. You need to place your whole logic into a subquery, and left join to this:
SELECT s.NewSeverity AS 'Severity'
,COUNT(WI.microsoft_vsts_common_severity) AS 'Total'
FROM ( VALUES
('Critical','I-High')
,('High','I-High')
,('Medium','I-Low')
,('Low','I-Low')
)s(OldSeverity,NewSeverity)
LEFT JOIN
( SELECT wi.Severity
FROM DimWorkItem WI (NOLOCK)
JOIN dbo.DimPerson P
ON p.personsk = WI.system_assignedto__personsk
JOIN DimTeamProject TP
ON WI.TeamProjectSK = TP.ProjectNodeSK
JOIN DimIteration Itr (NOLOCK)
ON Itr.IterationSK = WI.IterationSK
JOIN DimArea Ar (NOLOCK)
ON Ar.AreaSK = WI.AreaSK
WHERE TP.ProjectNodeName = 'ABC'
AND WI.System_WorkItemType = 'Bug'
AND WI.Microsoft_VSTS_CMMI_RootCause <> 'Change Request'
AND Itr.IterationPath LIKE '%\ABC\R1234\Test\IT%'
AND WI.System_State NOT IN ( 'Rejected', 'Closed' )
AND WI.System_RevisedDate = CONVERT(datetime, '9999', 126)
) WI
ON WI.Severity = s.OldSeverity
GROUP BY s.NewSeverity;