if you want to do sql queries on RDB files, it's probably better to just convert to a in-memory sqlite database and let sqlite do the queries (which should be easy to do for a tool that already support creating SQL Server tables from RDB files)
And maybe faster too, 20sec to load 30k entries is a bit slow ^^ (as you don't need additional stuff to make sql queries easier to implement, sqlite does that and probably with a better performance)
And joins would be possible with sqlite without super-complicated stuff
Another idea is to make a ODBC driver to read RDB. Then you can use a existing SQL IDE to make queries, copy data to another database (either another RDB, or a real SQL server), ...
But a ODBC driver is not that easy to do (but it would be the most powerful thing to do about RDB, all other stuff like queries, graphical interfaces, ... already exists)
It's like reading data.000, the best thing to do would be like windows explorer does with zip files, i.e. read data.000 as a folder (but again, it's far from easy to do

On another hand, on Linux (KDE) it's very easy and really great:

So any application can read any files without additional manipulation, and extracting/putting a file is just a copy/paste or drag/drop)
But as windows does not let us to do great stuff without overcomplicated code, Raskim's tool is still a great tool ^^
(maybe too much digress lol)
@undergroundtaffy
What i mean is to make a GUI without RDB structures inside, but use external file to describe a RDB so your GUI can display it and possibly convert it to a SQL table for example. So if there is a new RDB file that the tool can read, just make a new file that describe it and now the tool can read it and convert it to a SQL table. Like mine in fact : o (but mine is really focused on RDB files, nothing else)
So if structure.dll is a opensource DLL which anyone can create and the .exe does not know about RDB formats itself, then yes it's what i mean too
@Raskim
You should post screen shots in your first post, to have a fast view of your tool instead of lines of text, a bit like you made with the preview ^^