SQL how to put values on one line - sql

Question

It is necessary that in the second column in a single line should be all related accounts.
This shows an error
Conversion failed when converting the varchar value ',' to data type int.
SELECT [UserID],
STUFF((SELECT ', ' + UserID
FROM #RelatedIDs
WHERE (UserID = t.UserID)
FOR XML PATH('')) ,1,1,'') AS RelIDs
FROM #RelatedIDs t
GROUP BY UserID

Answer 1

You could cast the integer value to a varchar:
SELECT [UserID],
STUFF((SELECT ',' + CAST(UserID as VARCHAR(100))
FROM #RelatedIDs
WHERE (UserID = t.UserID)
FOR XML PATH('')) ,1,1,'') AS RelIDs
FROM #RelatedIDs t
GROUP BY UserID
If you are running a recent version of SQL Server (2017 or higher), you can get the same result in a much less obsfucated manner with string_agg():
SELECT t.UserID, STRING_AGG(r.UserID, ',') RelIDs
FROM #RelatedIDs t
INNER JOIN #RelatedIDs r on r.UserID = t.UserID
GROUP BY t.UserID
With the query put this way, it is plain to see that it makes little sense. The self-join operates on the same column as the one that defines the group, so this will just generate a list of identical UserIDs in column RelIDs (one per occurence of the given UserID in the original query).

Answer 2

Use CONCAT() instead of +:
SELECT [UserID],
STUFF((SELECT CONCAT(', ', UserID)
FROM #RelatedIDs ri
WHERE ri.UserID = t.UserID
FOR XML PATH('')
), 1, 2, '') AS RelIDs
FROM #RelatedIDs t
GROUP BY UserID;
Notice that I also changed the stuff arguments from 1, 1 to 1, 2. That is because you have a space after the comma.
Your correlation clause also suggests that the results will not be very interesting, when you get this to work.