Concatenate Columns in Stored Procedure
Use FOR XML PATH

Sample from TSQL – Concatenate Rows using FOR XML PATH() - sqlandme.com

SELECT      CAT.Name AS [Category],
            STUFF((    SELECT ',' + SUB.Name AS [text()]
                        — Add a comma (,) before each value
                        FROM Production.ProductSubcategory SUB
                        WHERE
                        SUB.ProductCategoryID = CAT.ProductCategoryID
                        FOR XML PATH('') — Select it as XML
                        ), 1, 1, '' )
                        — This is done to remove the first character (,)
                        — from the result
            AS [Sub Categories]
FROM  Production.ProductCategory CAT


Without FOR XML PATH



With FOR XML PATH