代码点火器和'两次'组

I have following query in CodeIgniter:

    $this->db
->select($this->vehicle_table.'.idvehicle, mark, type')
->group_by('mark')
->order_by('vehicles.mark', "desc")
->get($this->vehicle_table)
->result_array();

In my table I have record like:

type: auto mark: VW

and

type: bus mark: VW

This query works fine, but I'm getting only record (for VW) where type:auto, this query is ignoring type: bus

I have to "group by" two columns, right?

How should I write query to reach records separately by type and mark ?

edit

Solved, i added "->group_by('type')" before "->group_by('mark')".

Sory for that question, it was easy :)

Yes, you need to group by two columns.

In CI's Active Records, you just make it an array:

...
->group_by(array('mark', 'type'))
...

This will produce: GROUP BY mark, type

See the docs here: http://ellislab.com/codeigniter/user-guide/database/active_record.html