SQL Dynamic join?

Please see http://sqlfiddle.com/#!3/2506f/2/0

I have two tables. One is a general record, and the other is a table containing related documents that link to that record.

In my example I've created a straightforward query which shows all records and their associated documents. This is fine, but I want a more complex situation.

In the 'mainrecord' table there is a 'multiple' field. If this is 0, then I only want the most recent document from the documents table (that is, with the highest ID). If it is 1, I want to join all linked documents.

So, rather than the result of the query being this:-

ID  NAME    MULTIPLE    DOCUMENTNAME    IDLINK
1   One     1           first document    1
1   One     1           second document   1
2   Two     0           third document    2
2   Two     0           fourth document   2
3   Three   1           fifth document    3
3   Three   1           sixth document    3

It should look like this:-

ID  NAME    MULTIPLE    DOCUMENTNAME    IDLINK
1   One     1           first document    1
1   One     1           second document   1
2   Two     0           fourth document   2
3   Three   1           fifth document    3
3   Three   1           sixth document    3

Is there a way of including this condition into my query to get the results I'm after. I'm happy to explain further if needed.

Thanks in advance.

WITH myData
AS
(SELECT mainrecord.*, documentlinks.documentName, documentlinks.idlink,
Row_number()
                  OVER (
                    partition BY mainrecord.ID
                    ORDER BY mainrecord.ID ASC) AS ROWNUM
FROM mainrecord INNER JOIN documentlinks
ON mainrecord.id = documentlinks.idlink)
SELECT *
FROM mydata o
WHERE multiple = 0 AND rownum =
(SELECT max(rownum) FROM mydata i WHERE i.id = o.id)
UNION
SELECT *
FROM myData
WHERE multiple = 1

http://sqlfiddle.com/#!3/2506f/57