I could be wrong but it looks like you are running a select where the colum 'Data' = 'value', and then looping threw and storing the values of the Data colum.. Won't all the values of 'Data' be 'value' since thats what you queried for?

my %DataHash;
#get all values where the 'Data' colume = 'value'...?
my $sth = $dbh->prepare(" select ID, Data from table_name where Data=\
+"value\" ");
$sth->execute;
while ( my ( $ID, $Data) = $sth->fetchrow ) {
  $CountryDisplay{$ID} = "$Data";  # storing Data colum
} # end-while
$sth->finish
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I don't see the point in this whole loop in that case. I dunno if this was just because of the way you made the script smaller or what but I thought i would point it out.