Conditional Join or ignore results when second value is null - sql

Question

I've tried to focus on just the portion of my main query giving me trouble. This query is being used to populate an SSRS report which has an optional date parameter. This query snippet is used in a LEFT Join. If no date is specified, all matching records should be returned. That seems to work. But if I specify a date and no records are returned in the second column, no results for that row should be displayed. Not sure if I explained that well.
Here is the snippet:
DECLARE #DispoStartDt datetime, #DispoEndDt datetime, #DispoCode varchar(800)
SET #DispoStartDt = '5-1-2050'
--SET #DispoEndDt = '12-31-2014'
SET #DispoCode = '_NULL'
SELECT c1.CaseID,
STUFF((SELECT '; ' + CONVERT(VARCHAR(10), ct.DispoDt, 101)
FROM jw50_CountInvPers ct
WHERE ct.CaseID = '00-100'
AND (ct.DispoDt >= DATEADD(dd, DATEDIFF(dd, 0, ISNULL(#DispoStartDt, ct.DispoDt)), 0) AND ct.DispoDt < DATEADD(dd, DATEDIFF(dd, -1, ISNULL(#DispoEndDt, ct.DispoDt)), 0))
ORDER BY DispoDesc
FOR XML PATH('')), 1, 1, '') [DispoDts]
FROM jw50_Case c1
WHERE c1.CaseID = '00-100'
GROUP BY c1.CaseID
My results are:
CaseID DispoDts
00-100 NULL
I want no records returned if DispoDts is NULL. Since I cannot reference a column alias, is there another way than putting this in a sub select?
EDIT:
Here is the snippet used in my Join. I'm getting rows with NULL DispoDts because of the left join. If I specify a start date, I want the results to be treated like an inner join, only return results where they match a join row. If I don't specify a date, give me everything in the main table if a join exists or not.
DECLARE #DispoStartDt datetime, #DispoEndDt datetime, #DispoCode varchar(800)
SET #DispoStartDt = '5-1-2015'
--SET #DispoEndDt = '12-31-2014'
SET #DispoCode = '_NULL'
SELECT c.CaseID
, c.ProsNum AS FileNum
, c.CaseStatusDesc AS CaseStatus
, disp.DispoDts
FROM jw50_Case c
LEFT JOIN (SELECT CaseID, DispoDts
FROM (
SELECT c1.CaseID,
STUFF((SELECT '; ' + CONVERT(VARCHAR(10), ct.DispoDt, 101)
FROM jw50_CountInvPers ct
WHERE ct.CaseID = c1.CaseId
AND (ct.DispoDt >= DATEADD(dd, DATEDIFF(dd, 0, ISNULL(#DispoStartDt, ct.DispoDt)), 0) AND ct.DispoDt < DATEADD(dd, DATEDIFF(dd, -1, ISNULL(#DispoEndDt, ct.DispoDt)), 0))
ORDER BY DispoDesc
FOR XML PATH('')), 1, 1, '') [DispoDts]
FROM jw50_Case c1
WHERE c1.CaseID = c1.CaseId
GROUP BY c1.CaseID
) a
WHERE DispoDts IS NOT NULL
) disp ON disp.CaseID = c.CaseID
ORDER BY CaseID, DispoDts
EDIT 2:
Ok, feels dirty, but it works.
WHERE (#DispoStartDt IS NULL AND #DispoEndDt IS NULL)
OR (#DispoStartDt IS NOT NULL AND #DispoEndDt IS NOT NULL AND disp.DispoDts IS NOT NULL)
OR (#DispoStartDt IS NOT NULL AND #DispoEndDt IS NULL AND disp.DispoDts IS NOT NULL)
OR (#DispoStartDt IS NULL AND #DispoEndDt IS NOT NULL AND disp.DispoDts IS NOT NULL)

Answer 1

You can try:
DECLARE #DispoStartDt datetime, #DispoEndDt datetime, #DispoCode varchar(800)
SET #DispoStartDt = '5-1-2050'
--SET #DispoEndDt = '12-31-2014'
SET #DispoCode = '_NULL'
SELECT CaseID,
[DispoDts]
FROM (
SELECT c1.CaseID,
STUFF((SELECT '; ' + CONVERT(VARCHAR(10), ct.DispoDt, 101)
FROM jw50_CountInvPers ct
WHERE ct.CaseID = '00-100'
AND (ct.DispoDt >= DATEADD(dd, DATEDIFF(dd, 0, ISNULL(#DispoStartDt, ct.DispoDt)), 0) AND ct.DispoDt < DATEADD(dd, DATEDIFF(dd, -1, ISNULL(#DispoEndDt, ct.DispoDt)), 0))
ORDER BY DispoDesc
FOR XML PATH('')), 1, 1, '') [DispoDts]
FROM jw50_Case c1
WHERE c1.CaseID = '00-100'
GROUP BY c1.CaseID
) as tbaux
WHERE [DispoDts] IS NOT NULL
This way you get the same values ​​as before, but the result is passed to a query above which validates the DispoDts
And this way ?
DECLARE #DispoStartDt datetime, #DispoEndDt datetime, #DispoCode varchar(800)
SET #DispoStartDt = '5-1-2015'
--SET #DispoEndDt = '12-31-2014'
SET #DispoCode = '_NULL'
SELECT c.CaseID
, c.ProsNum AS FileNum
, c.CaseStatusDesc AS CaseStatus
, disp.DispoDts
FROM jw50_Case c
LEFT JOIN (SELECT c1.CaseID,
STUFF((SELECT '; ' + CONVERT(VARCHAR(10), ct.DispoDt, 101)
FROM jw50_CountInvPers ct
WHERE ct.CaseID = c1.CaseId
AND (ct.DispoDt >= DATEADD(dd, DATEDIFF(dd, 0, ISNULL(#DispoStartDt, ct.DispoDt)), 0) AND ct.DispoDt < DATEADD(dd, DATEDIFF(dd, -1, ISNULL(#DispoEndDt, ct.DispoDt)), 0))
ORDER BY DispoDesc
FOR XML PATH('')), 1, 1, '') [DispoDts]
FROM jw50_Case c1
WHERE c1.CaseID = c1.CaseId
GROUP BY c1.CaseID
) disp ON disp.CaseID = c.CaseID
WHERE #DispoEndDt IS NULL OR disp.DispoDts IS NOT NULL
ORDER BY CaseID, DispoDts