You are mixing a statement handler with its result.
$subs_rst = $subs_str->execute(); # execute subnet select
This instruction returns the execution result, i.e. if the query was executed correctly. (See the DBI docs).
For your fetch statement you need to use $subs_str, i.e.the statement handler.
As a side note, be aware that the execute method DOES NOT return the number of rows for a SELECT query.
Moreover (this is not related to your problem, but it can create other unpleasant side effects) you should not interpolate variables in your queries, but use placeholders instead.
By deleting the original content, you made this answer - and the other ones below - almost meaningless. It's a pity, because the value of a PerlMonks node is in the question as much as in the answer. Other people can benefit from your mistakes. Don't be ashame of that. Everybody makes mistakes. The important thing is to learn from them, so please put the question back in place.
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