How to Concatenate User Names from Multiple Records in T-SQL Using FOR XML PATH()?

Efficiently Combining User Names in T-SQL with FOR XML PATH()

Challenge: We need to combine user names from multiple records within a complex database structure involving multiple tables with many-to-many relationships. The objective is to display data from two tables while concatenating names from a third, creating a comma-separated list of user first names (FName) associated with each review.

Solution: Leveraging FOR XML PATH()

The FOR XML PATH() method offers a concise solution for this string concatenation task. Here's the T-SQL code:

SELECT  *,
        ( 
            SELECT  u.FName + ','
            FROM    @Users u INNER JOIN 
                    @Reviewers rs ON u.UserID = rs.UserID
            WHERE   rs.ReviewID = r.ReviewID
            FOR XML PATH('')
        ) AS UserNames
FROM    @Reviews r

Breakdown:

• The main SELECT statement retrieves all columns (*) from the @Reviews table.
• The nested SELECT statement performs the concatenation. It joins the @Users and @Reviewers tables using UserID to link users to reviews.
• The WHERE clause filters the users to include only those associated with the current review (matching ReviewID).
• FOR XML PATH('') converts the concatenated FName values into a single XML string, effectively creating a comma-separated list (the trailing comma will need to be handled, see below).
• The result is assigned to the UserNames column.

Output and Refinement:

This query generates the desired result: each review's details (ReviewID, ReviewDate, etc.) are displayed alongside a comma-separated list of associated user first names. To remove the trailing comma, you can use a STUFF function:

SELECT  *,
        STUFF(( 
            SELECT  ',' + u.FName
            FROM    @Users u INNER JOIN 
                    @Reviewers rs ON u.UserID = rs.UserID
            WHERE   rs.ReviewID = r.ReviewID
            FOR XML PATH('')
        ), 1, 1, '') AS UserNames
FROM    @Reviews r

This improved version uses ',' u.FName to prepend a comma, and then STUFF removes the leading comma, providing a clean comma-separated list of user names.

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