If you know the keys are unique within each table, one shortcut might be to notice the second time you saw each key in a scan of both: 
my @dups = do {
  my %count;
  grep ++$count{$_} == 2, @keys_from_one, @keys_from_two;
};

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-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.

In reply to •Re: Finding duplicate keys by merlyn
in thread Finding duplicate keys by Wally Hartshorn

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