Creating Subframe of Frame with zero rows

[tomschw]

The constructor, which creates a Frame around the sub-frame of another Frame, throws an error, if the Frame has no rows, even if the new Frame should also have zero rows.

Code example:

f = createFrame(
    [1, 10, 20],
    "temp");

registerView("sample", f);

k = sql("select sample.temp from sample
 where sample.temp <= 0;");

print(k);

The compiler first creates a filter row Kernel, which returns a frame with zero rows. Then it calls Kernel to extract the column temp from that frame, which throws the aforementioned error.

[pdamme]

Thanks for reporting this bug, @tomschw. I can reproduce it.

[pdamme]

JFYI: While looking into this issue and your PR #496, I discovered that this is actually just a special case of a more general bug. I've opened a new issue #504 specifically for that.