Answers for "rails migration to clear a column"

rails remove column from model

class RemoveCountryFromSampleApps < ActiveRecord::Migration[5.0]
  def change
    remove_column :sample_apps, :country, :string
  end
end

rails migration remove column

rails g migration Remove..From.. col1:type col2:type col3:type

#Exemple :

rails g migration RemoveCountryFromSampleApps country:string