Flatten association table to multi-value column?

Question

I have a table with just product ID\'s and category ID\'s (products can be in more than one category). How can I flatten the category ID\'s into a product column so I end us

Answer 1

I would suggest using a Recursive CTE. I believe that it would be something like this:

select productid, categoryid, 
    row_number() over (partition by id order by categoryid) as rownum
into #tabletorecurse
from TABLENAME

with finaloutput as
(
    select productid as id, name, desc, categoryid as categories, rownum
    from #tabletorecurse
        join PRODUCTTABLE
            on PRODUCTTABLE.id = #tabletorecurse.productid
    where rownum = 1

    union all

    select tr.id, tr.name, tr.desc, 
        finaloutput.categories + ', ' + tr.categoryid, tr.rownum
    from #tabletorecurse as tr
        join finaloutput 
            on finaloutput.rownum + 1 = tr.rownum 
                and finaloutput.id = tr.productid
)
select id, name, desc, categories
from finaloutput
    join 
    (
        select max(rownum) as maxrow, id
        from finaloutput
        group by id 
    ) as maxvalues
       on maxvalues.id = finaloutput.id 
           and maxvalues.maxrow = finaloutput.rownum