Just seems to me to be a simple group by:
CREATE TABLE #temp (
    prodID int,
    mktID nvarchar(255),
    rev decimal,
    qty decimal,
    UNIQUE CLUSTERED
        (
        mktID ASC,
        prodID ASC
        )

Unless your encryption process can be proven to be capable of being decrypted by the process at the other end, it seems unlikely this would work unless you had SQL...

One additional note on JOINs...  Once you grasp the basics, you can start using GROUP BY to restrict the rows that are returned, and that will then allow you to...

I'm not sure that's possible unless you have some kind of DDL trigger or monitoring in place.   So if you weren't already getting such information, you may or may not...

Just an fyi ... If memory serves me correctly, sp_cursorprepexec is there to get ready to serve up the result set as a cursor that your application can "hold on...

Slowness in the disk subsystem ?   Do you have any I/O waits going on ?   Are you cramped for disk space ?