Doctrine 1.2 must have at least one field selected Error.but one is actually selected

Question

Hello Good People!

i've been banging my head against the wall over the past hour about this Exception :

The root class of the query (alias b) must have at least one field selected

on a small school hotel booking project here is the part of the schema concerned

RoomType:
  actAs: [Timestampable]
  tableName: room_type
  columns:
    name: string(100)
    number_of_bed: integer

Room:
  tableName: room
  columns:
    id:
      type: string(36)
      primary: true
    room_number: integer
    price: decimal
  relations:
    RoomType:
      class: RoomType
      local: type_id
      foreign: id

RoomBooking:
  tableName: roombooking
  actAs: [Timestampable]
  columns:
    id:
      type: string(36)
      primary: true
      room_id: string(36)
      checkin_date: date
      checkout_date: date
      is_cancelled: boolean
  relations:
    Room:
      class: Room
      local: room_id
      foreign: id

i tripped out certain field for sake of simplicity and having short post.So basically i wanted to query for the total, the type of rooms booked each day of a certain month.i wanted things simple so for now i assumed booking are just for 24 hours so for now i'm just looking at checkin date.here is the query

$q = Doctrine_Query::create ()
->select("SUM(COUNT(b.id)), b.checkin_date as DATE, t.name")
->from ("Hotel_Model_RoomBooking b" )
->leftJoin("b.Room r")
->leftJoin("r.RoomType t")
->where ("b.checkin_date > ? AND b.checkin_date < ?", array ($first, $last))
->groupBy("b.checkin_date, t.name");

$result = $q->fetchArray ();    

b.checkin_date is one field of the root class so i have this and b.id selected, and up to now i can't figure it out.What do you think? what am i doing wrong here? thanks for reading and thanks in advance for your help