In a migration I have this following: " t.integer :post_count" where can I found in the doc all the attribute that I can give to 'post_*' so that Rails will make the proper sql statement. I mean can I have a t.integer :post_avg ?

20130923163537_create_categories.rb

class CreateCategories < ActiveRecord::Migration
  def change
    create_table :categories do |t|
      t.string :name, null: false
      t.string :slug, null: false
      t.integer :post_count, default: 0

      t.timestamps
    end
  end
end