hello guys!

I have a hash of hashes, for example:

%hash = {
         abc => {
                 def => 1,
                },
         ghi => {
                 jkl => 1,
                },
};
[download]

What happen if I do:

delete($hash{abc}{def});
[download]

am I staying with?:

%hash = {
         abc => undef,
         ghi => {
                 jkl => 1,
                 mno => 1,
                },
};
[download]

That was the first question.
My second one is, I'm looping over the hash and delete keys as shown above if fulfilled a condition. If the ansewer to the first question is yes, is there a short way to delete also the first level key ('abc' in the example) when deleted all second level keys under it. In the example, when performing the above delete, i would have like to stay with:?:

%hash = {
         ghi => {
                 jkl => 1,
                 mno => 1,
                },
};
[download]

Thanks