Merge duplicate records into 1 field

Question

I have a database table that contains a list of contacts, some of those contacts might have multiple records, e.g.

CustomerID, CustomerName, Vehicle
1, Dan,          


        

Answer 1

There are some nice answers to this problem on another question.

According to the linked article, this will only work in SQL Server 2005 onwards due to the use of the XML functions. From the article -

SELECT table_name, 
       LEFT(column_names,LEN(column_names) - 1)   AS column_names 
FROM   (SELECT table_name, 
               (SELECT column_name + ',' AS [text()] 
                FROM   information_schema.columns AS internal 
                WHERE  internal.table_name = table_names.table_name 
                FOR xml PATH ('') 
               ) AS column_names 
        FROM   (SELECT   table_name 
                FROM     information_schema.columns 
                GROUP BY table_name) AS table_names) AS pre_trimmed;

Second version (admittedly inspired by this post, which I stumbled on after writing the first version):

SELECT table_name, 
       LEFT(column_names,LEN(column_names) - 1)   AS column_names 
FROM   information_schema.columns AS extern 
       CROSS APPLY (SELECT column_name + ',' 
                    FROM   information_schema.columns AS intern 
                    WHERE  extern.table_name = intern.table_name 
                    FOR XML PATH('') 
                   ) pre_trimmed (column_names) 
GROUP BY table_name,column_names;

The second CROSS APPLY version is supposedly slower according to the execution plan, but I didn’t conduct any benchmarks at all.