Why not? But if your schema is so secret, come up with a simple one for use in interviews.
> You also assume they know SQL
I specifically said this was for a c++/sql job.
> so you are fine with hiring someone who can write a select only with the help of google
No, I'm not fine with that, even if it were do-able.
> I can learn your language quickly (even C++ is not that hard - the dark corners means it takes years to become great but to be productive doesn't take very long)
Wrongo. And not just for C++.
> I don't want to force any particular language on the interview, I want something that proves they can write code.
Why not? But if your schema is so secret, come up with a simple one for use in interviews.
> You also assume they know SQL
I specifically said this was for a c++/sql job.
> so you are fine with hiring someone who can write a select only with the help of google
No, I'm not fine with that, even if it were do-able.
> I can learn your language quickly (even C++ is not that hard - the dark corners means it takes years to become great but to be productive doesn't take very long)
Wrongo. And not just for C++.
> I don't want to force any particular language on the interview, I want something that proves they can write code.
Obviously, we want very different things.