Unable to use SQL select with includes

class SlotBooking < ApplicationRecord
  belongs_to :booking
  belongs_to :slot

  delegate :start_time, :end_time, to: :slot

  validates :price, presence: true
end

class Slot < ApplicationRecord
  belongs_to :program
  has_many :slot_bookings, dependent: :destroy
end
a = SlotBooking.includes(:slot).select("to_char(slots.start_time, 'mm/dd/yy') as start_date").ref
erences(:slots)
a.first.start_date

yields following output