Create initial migration sans user table.
user
```ruby
class InitialMigration < ActiveRecord::Migration
  def change
    create_table :links do |t|
      t.string :uri
      t.integer :upvote_count
      t.integer :downvote_count

      t.timestamps null: false
    end
    
    create_table :tags do |t|
      t.string :name
      t.integer :sequence

      t.timestamps null: false
    end
    
    create_table :links_tags do |t|
      t.belongs_to :links, index: true
      t.belongs_to :tags, index: true
    end
    
    create_table :comments do |t|
      t.belongs_to :link, index: true
      t.string :body
      
      t.timestamps null: false
    end
  end
end
```
assistant