I guess my understanding of sort leaves much to be desired. Here is the code I am using to build the hash. 
while (my $row = $sth->fetchrow_hashref) {
      $$patients{$row->{'pat_id'}} ||= {
          first_name => "$row->{'first_name'}",
          last_name => "$row->{'last_name'}",
          dme_num => "$row->{'dme_num'}",
          dme_pid => "$row->{'dme_pid'}",
          phone => "$row->{'phone'}",
          pid => "$row->{'pat_id'}"
      };
      my $hash = {
        file_name => "$row->{'file_name'}",
        file_type => "$row->{'file_type'}",
        date_uploaded => "$row->{'date_uploaded'}",
        date_faxed => "$row->{'date_faxed'}"
      };
      push(@{$$patients{$row->{'pat_id'}}->{files}}, $hash);
      if (($row->{'date_uploaded'} < $$patients{$row->{'pat_id'}}->{'o
+ld_file'}) or (!$$patients{$row->{'pat_id'}}->{'old_file'}))  {
         $$patients{$row->{'pat_id'}}->{'old_file'} = $row->{'date_upl
+oaded'};
      }
      $x++;
}

[download]
This below doesn't error but it is not carrying the rest of the data attached with it. 
my %sorted =
sort { $patients->{$a}{old_file} cmp $patients->{$b}{old_file} }
   (keys %{$patients});
my $patients = \%sorted;
# or put { } around the sort expression to do it one line.

[download]
or 
sort { $$patients{$a}->{old_file} cmp $$patients{$b}->{old_file} }

[download]
And for some odd reason $patients is no longer a hash ref??

In reply to Re^4: Sorting a Hash Ref by bkiahg
in thread Sorting a Hash Ref by bkiahg

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.