Question

I’m using a generic system for reporting which takes data from a database view (SQL Server 2005). In this view I had to merge data from one-to-many relations in one row and used the solution described by priyanka.sarkar in this thread: Combine multiple results in a subquery into a single comma-separated value. The solution uses SQLXML for merging the data (subquery):

SELECT STUFF(
    (    SELECT ', ' + Name 
         FROM MyTable _in 
         WHERE _in.ID = _out.ID 
         FOR XML PATH('')),        -- Output multiple rows as one xml type value,
                                   -- without xml tags
    1, 2, '')      -- STUFF: Replace the comma at the beginning with empty string
FROM MyTable _out 
GROUP BY ID        -- Removes duplicates

That works perfectly (it’s not even that heavy in performance) except my data now gets XML encoded (& => & etc.) by SQLXML -I didn’t want XML data after all, I just used this as a trick- and because of the generic system I can’t code around this to clean it up so the encoded data goes straight to the report. I can’t use stored procedures with the generic system so CURSOR-merging or COALESCE-ing is not an option here…

So what I’m looking for is a manner in T-SQL that lets me decode the XML again, or even better: avoids SQLXML from encoding it. Obviously I could write a stored function that does this, but I’d prefer a built-in, more safe manner…

Thanks for your help…

Answer 1

If you specify type as an option to for xml, you can use an XPath query to convert the XML type back to a varchar. With an example table variable:

declare @MyTable table (id int, name varchar(50))

insert @MyTable (id, name) select 1, 'Joel & Jeff'
union all select 1, '<<BIN LADEN>>'
union all select 2, '&&BUSH&&'

One possible solution is:

select  b.txt.query('root').value('.', 'varchar(max)')
from    (
        select  distinct id
        from    @MyTable
        ) a
cross apply
        (
            select  CASE ROW_NUMBER() OVER(ORDER BY id) WHEN 1 THEN '' 
                        ELSE ', ' END + name
        from    @MyTable
        where   id = a.id
        order by 
                id
        for xml path(''), root('root'), type
        ) b(txt)

This will print:

Joel & Jeff, <<BIN LADEN>>
&&BUSH&&

Here’s an alternative without XML conversions. It does have a recursive query, so performance mileage may vary. It’s from Quassnoi’s blog:

;WITH   with_stats(id, name, rn, cnt) AS
        (
        SELECT  id, name,
                ROW_NUMBER() OVER (PARTITION BY id ORDER BY name),
                COUNT(*) OVER (PARTITION BY id)
        FROM    @MyTable
        ),
        with_concat (id, name, gc, rn, cnt) AS
        (
        SELECT  id, name,
                CAST(name AS VARCHAR(MAX)), rn, cnt
        FROM    with_stats
        WHERE   rn = 1
        UNION ALL
        SELECT  with_stats.id, with_stats.name,
                CAST(with_concat.gc + ', ' + with_stats.name AS VARCHAR(MAX)),
                with_stats.rn, with_stats.cnt
        FROM    with_concat
        JOIN    with_stats
        ON      with_stats.id = with_concat.id
                AND with_stats.rn = with_concat.rn + 1
        )
SELECT  id, gc
FROM    with_concat
WHERE   rn = cnt
OPTION  (MAXRECURSION 0)