return 1 row from multiple case statements - sql-server

Question

In the following Query below in the port with the case statements I'm trying to figure out how to not return a null value when the SegmentType doesn't match.
QRSubscriberTag,MLKSubscriberTag, QTMSubscriber Tag, are actually a table of Tags uniquely identified by their SegID and a segmentType associated to the SegID. I use an outer apply with a subquery that calls FOR XML PATH('') to concatenate the Tags together related to the specific tag.
The flaw with this method is that when the Tag isn't for example QRSubscriberTag, then a null record in the QRSubscriberTag column is created.
QRSubscriberTag|QR01|MLKSubscriberTag|MLK01|QTMSubscriberTag|QTM01|QTM02
NULL |NULL|NULL |{Data}|null |FH |45
TKP ;OCP ;OCR ;|R |NULL |null |null |null |null
What I would like to see is all the Data in 1 line
QRSubscriberTag|QR01|MLKSubscriberTag|MLK01|QTMSubscriberTag|QTM01|QTM02
TKP ;OCP ;OCR ;|R |NULL |{Data}|null |FH |45
Below is my code
SET NOCOUNT ON
USE [Apps]
SELECT [BusRuleEnforceID], [FormatType], [Format],
[tag], [TagValue], Operator,
[QRSubscriberTag],[QR01],
[MLKSubscriberTag],[MLK01],
[QTMSubscriberTag],[QTM01],[QTM02]
FROM
(
SELECT
DISTINCT main.BusRuleEnforceID,
main.FormatType,
main.Format,
main.tag,
main.TagValue,
main.Operator,
CASE
WHEN seg.SegmentType = 'QR' THEN LEFT(SegsubscriberTags.list, LEN(SegsubscriberTags.list))
END AS [QRSubscriberTag],
CASE
WHEN seg.SegmentType = 'MLK' THEN LEFT(SegsubscriberTags.list, LEN(SegsubscriberTags.list)-1)
END AS [MLKSubscriberTag],
CASE
WHEN seg.SegmentType = 'QTM' THEN LEFT(SegsubscriberTags.list, LEN(SegsubscriberTags.list)-1)
END AS [QTMSubscriberTag],
c.ItemName as [SegmentId],
Case
WHEN c.ItemValue is not null and len(rtrim(c.ItemValue)) > 0 THEN c.ItemValue
ELSE LEFT(TagOptions.list, LEN(TagOptions.list)-1)
END as [Tags]
FROM
BMT_BusRulemaineria main
LEFT OUTER JOIN
BMT_BusRuleServiceType st
ON st.MappingmaineriaID = main.BusRuleEnforceID
LEFT OUTER JOIN
BMT_BusRuleSegment seg
ON seg.BusRuleEnforceID = main.BusRuleEnforceID
LEFT OUTER JOIN
BMT_BusRuleItem c
ON c.BusRuleEnforceSegID = seg.BusRuleEnforceSegID
LEFT OUTER JOIN
BMT_BusRuleItemOption co
ON c.BusRuleItemId = co.BusRuleItemId
OUTER APPLY
(
SELECT
IsNull(co2.Tag, '{Unknown}') + ISNULL('=' + co2.TagValue, '') + ':' + IsNull(co2.ItemValue, '')+ ';' AS [text()]
FROM
BMT_BusRuleItemOption co2
WHERE
co.BusRuleItemId = co2.BusRuleItemId
ORDER BY
co2.BusRuleItemId
FOR XML PATH('')
) TagOptions (list)
OUTER APPLY
(
SELECT
IsNull(porttag.Tag, '{Unknown}') + ' ' + ISNULL(porttag.Operator, '') + ' ' + IsNull(porttag.TagValue, '') + ';' AS [text()]
FROM
BMT_BusRuleSegmentTag porttag
WHERE
seg.BusRuleEnforceSegID = porttag.BusRuleEnforceSegID
ORDER BY
porttag.BusRuleEnforceSegID
FOR XML PATH('')
) SegsubscriberTags (list)
WHERE main.BusRuleEnforceID = 632563
AND main.TagTypeId = 1
) AS QRSourceTable
PIVOT
(
max([Tags])
FOR [SegmentId] IN ([QR01], [MLK01], [QTM01], [QTM02])
) AS QRPivotTable
ORDER BY
[TagTypeId], [BusRuleEnforceID]
EDIT: Full Result Set
Note: QRSubscriber, MLKSubscriber, and QTMSubscriber tags all have unique SegIDs.
<table><tbody><tr><th>FormatType</th><th>Format</th><th>Version</th><th>AmtCode</th><th>Date</th><th>LocationIdentifier</th><th>TagType</th><th>tag</th><th>TagValue</th><th>Operator</th><th>InfoCode</th><th>QRSubscriberTag</th><th>QR01</th><th>QR02</th><th>QR03</th><th>QR04</th><th>QR05</th><th>QR06</th><th>QR07</th><th>MLKSubscriberTag</th><th>MLK01</th><th>QTMSubscriberTag</th><th>QTM01</th><th>QTM02</th></tr><tr><td>DN</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>TIR</td><td>RPSAMN</td><td>NULL</td><td>exists</td><td>78</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>{Data}</td><td>NULL</td><td>TRH</td><td>675</td></tr><tr><td>DN</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>TIR</td><td>RPSAMN</td><td>NULL</td><td>exists</td><td>78</td><td>TKRARAP not exists TKRALAP not exists TKRADAP not exists </td><td>J</td><td>SKU</td><td>34</td><td>NULL</td><td>NULL</td><td>SILMULTU:2;SILMHLTU:67</td><td>TOPALD:{Data};QORITK{Data}</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td><td>NULL</td></tr></tbody></table>

Answer 1

Use the ELSE clause to assign a default value when the comparison does not match, like so:
CASE WHEN port.SegmentType = 'QR' THEN
LEFT(SegDependantTags.list, LEN(SegDependantTags.list))
ELSE 'Your Value Rather Than NULL Goes Here'
END AS [QRSubscriberTag],

Answer 2

It seems that instead of using Distinct in your QRSourceTable sub-query you want to use a Group By with a MAX aggregate function on your subscriber tag fields:
SELECT
main.BusRuleEnforceID,
main.FormatType,
main.Format,
main.tag,
main.TagValue,
main.Operator,
max(CASE
WHEN port.SegmentType = 'QR' THEN LEFT(SegDependantTags.list, LEN(SegDependantTags.list))
END) AS [QRSubscriberTag],
max(CASE
WHEN port.SegmentType = 'MLK' THEN LEFT(SegDependantTags.list, LEN(SegDependantTags.list)-1)
END) AS [MLKSubscriberTag],
max(CASE
WHEN port.SegmentType = 'QTM' THEN LEFT(SegDependantTags.list, LEN(SegDependantTags.list)-1)
END) AS [QTMSubscriberTag],
c.ItemName as [SegmentId],
Case
WHEN c.ItemValue is not null and len(rtrim(c.ItemValue)) > 0 THEN c.ItemValue
ELSE LEFT(TagOptions.list, LEN(TagOptions.list)-1)
END as [Tags]
from
...
WHERE main.BusRuleEnforceID = 632563
AND main.TagTypeId = 1
GROUP BY main.BusRuleEnforceID,
main.FormatType,
main.Format,
main.tag,
main.TagValue,
main.Operator