I may be mistaken, but I believe that DBI will re-use the hashref it gives back through fetch(). I would suggest using bind_columns() (and prepare_cached(), but that's another story). I'd rewrite your thing as such:

sub get_stuff_from_db
{
   my ($query) = @_;

   my $sth = $dbh->prepare_cached( $query )
      or die "Could not prepare '$query'\n";

   $sth->execute()
      or die "Could not execute '$query'\n";

   $sth->bind_columns(
      \(my ($x, $y, $z)) #Assumes three columns returned
   );

   my %results;
   while ($sth->fetch) {
      @results{qw(X Y Z)) = ($x, $y, $z);
   }

   $sth->finish;

   return \%results;
}
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A few notes:

• Use strict! Do _NOT_ use globals. (Unless, of course, you know why you shouldn't. Then, go right ahead. For example, $dbh is usually an acceptable global, if not desirable.)
• Pass your query in. This will allow you to reuse this function.
• You'll notice I'm checking the return values of my calls to DBI. Good production code will always do this, and for more than just DBI.
• I'm betting your query has variables in it. Use placeholders. That will allow for safer (and better) performance. (For example, do you know how to do all the quoting stuff? I don't, nor do I want to.)
• Instead of passing in a hashref, return a hashref. The function shouldn't know anything about how you're going to use its data. It should just know how to make it. This way, you can use the data in more than one way, as you need to.

------
We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.