If you have the need to take multiple rows into 1 comma separated row then this should do the trick. One of the biggest usages for this is when you’re using SSRS with multiple parameters.
DECLARE @COLUMNS VARCHAR(MAX)
SELECT @COLUMNS =
COALESCE (@COLUMNS + ‘,’ + CAST(FirstName AS NVARCHAR) + ”,” + CAST(FirstName AS NVARCHAR) + ”)