<p>I am re-designing an application for a ASP.NET CMS that I really don't like. I have made som improvements in performance only to discover that not only does this CMS use MS SQL but some users "simply" use MS Access database.</p>

<p>The problem is that I have some tables which I inner join, that with the MS Access version are in two different files. I am not allowed to simply move the tables to the other mdb file.</p>

<p>I am now trying to figure out a good way to "inner join" across multiple access db files?</p>

<p>It would really be a pity if I have fetch all the data and the do it programmatically!</p>

<p>Thanks</p>

If you have access to the MDBs, and are able to change them, you might consider using Linked Tables. Access provides the ability to link to external data (in other MDBs, in Excel files, even in SQL Server or Oracle), and then you can perform your joins against the links.
I'd strongly encourage performance testing such an option. If it's feasible to migrate users of the Access databases to another system (even SQL Express), that would also be preferable -- last I checked, there are no 64-bit JET drivers for ODBC anymore, so if the app is ever hosted in a 64-bit environment, these users will be hosed.