# Throw away all keys in old hash that are in new, update keys that ch
+anged or are new
foreach $key (keys %$new) {
    if (exists($old->{$key}) {
    if ($old->{$key} ne $new->{$key}) {
        updateindatabase($key,$new->{$key});
    }
    delete $old->{$key};
    }
    else {
    updateindatabase($key,$new->{$key});
    }

# remove keys that are only in old
foreach  $key (keys %$old) {
    deleteindatabase($key);
}
[download]

That should do it. I assume the hash is very big, otherwise simply deleting and just storing the new hash would be faster and simpler

Thanks for your efforts

I want to check only particular fields like sdrpretax_vcd taxamt_vcd sdrposttax_vcd dchdetaildate in $old and $new hashes. If there are any differences, I must update the values from $new hash. Please let me know if I can achieve in minimal steps rather than looping around the hashes...

foreach my $TAP ( keys %{$new} ) {
    ;
    if ( exists($old->{$TAP}) ) {
        ;
        my $hasUpdated = '0';

        foreach my $check_field ( qw(sdrpretax_vcd taxamt_vcd sdrpostt
+ax_vcd dchdetaildate) ) {
            ;
            if ( $new->{$TAP}->{$check_field} ne $old->{$TAP}->{$check
+_field} ) {
                ;
                $hasUpdated = 1;
                last;
            }
        }

        if ( $hasUpdated ) {
            print " Has to update the DB now ";
        }
    }
}
[download]

Why are your requirements changing all the time? Maybe you want this:

if ( exists $new->{$TAP}->{$check_field} and 
      (not exists  $old->{$TAP}->{$check_field} or $new->{$TAP}->{$che
+ck_field} ne $old->{$TAP}->{$check_field}) ) {
            $hasUpdated = 1;
            last;
}
[download]

while ( ($ko,$vo) = each %$old ) { 
   while ( ($kn,$vn) = each %$new ) {
     # compare
   }
}
[download]

of course there are other tricks possible like using hash slices or array slices of keys of hashes and so on...