rubytutorial.org microposts invalid SQL statement

home.rb

<% if signed_in? %>
  <table class="front" summary="For signed-in users">
    <tr>
      <td class="main">
        <h1 class="micropost">What's up?</h1>
        <%= render 'shared/micropost_form' %>
				<% unless @feed_items.empty? %>
					<%= render 'shared/feed' %>
				<% end %>
      </td>
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micropost.rb

class Micropost < ActiveRecord::Base
  attr_accessible :content
  
  belongs_to :user
  
  validates :content, :presence => true, :length => { :maximum => 140 }
  validates :user_id, :presence => true
  
  default_scope :order => 'microposts.created_at DESC'
  
  #Return microposts from the users being followed by the given user--
  scope :from_users_followed_by, lambda { |user| followed_by(user) }
  
  def self.from_users_followed_by(user)
    followed_ids = user.following.map(&:id).join(", ")
    where("user_id IN (#{followed_ids}) OR user_id = ?", user)
  end
  
  private
  
    #Return an SQL condition for users followed by the given user.
    #We include the user's own ID as well--
    def self.followed_by(user)
      followed_ids = %(SELECT followed_id FROM relationships
                       WHERE follower_id = :user_id)
      where("user_id IN (#{followed_ids}) OR user_id = :user_id",
            { :user_id => user })
    end
end

pages_controller.rb

class PagesController < ApplicationController
  def home
    @title = "Home"
    if signed_in?
      @micropost = Micropost.new
      @feed_items = current_user.feed.paginate(:page => params[:page])
    end
  end
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user.rb

class User < ActiveRecord::Base
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  def following?(followed)
    relationships.find_by_followed_id(followed)
  end
  
  def follow!(followed)
    relationships.create!(:followed_id => followed.id)
  end
  
  def unfollow!(followed)
    relationships.find_by_followed_id(followed).destroy
  end
  
  def feed
    Micropost.from_users_followed_by(self)
  end
  
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end