use somepackage;

my $conn = somepackage::connectdb();

$conn->{AutoCommit} = 0;

...

sub foo {
  my ($conn, $bar) = @_;
  my $sth = $conn->prepare(qq{
    SELECT COUNT(*) AS MYCOUNT FROM MYTABLE WHERE ID=?
  });
  $sth->execute($bar);
  my $ref = $sth->fetchrow_hashref();
  $sth->finish();
  return $ref->{MYCOUNT};
}

print &foo($conn, 'some id');

...

$conn->disconnect();

__END__