my($stmt2, @bind2) =
  $sql->select("users, drivers",
               ["users.username"],
               { "drivers.name" => "John",
                 "users.userid" => \"= drivers.userid"}
   );
print Dumper(\$stmt2, \@bind2);
# produces:
$VAR1 = \'SELECT users.username FROM users, drivers WHERE ( drivers.name = ? AND users.userid = drivers.userid )';
$VAR2 = [
          'John'
        ];