package Hue::SQL;
sub open { return DBI->connect blah blah; }
sub close { $main::dbh->disconnect; }          ##  <-- here is it: use $main::dbh

package Hue::Foo;
sub do_something {
    my $data = shift;
    $main::dbh->do ("sql query using \$data"); ##  <-- again
}

package main;
use Hue::SQL;
use Hue::Foo;
$dbh = Hue::SQL::open;
Hue::Foo::do_something ($data);