rails generate migration RemoveFieldNameFromTableName field_name:datatype
remove_column :table_name, :column_name
class RemoveCountryFromSampleApps < ActiveRecord::Migration[5.0]
def change
remove_column :sample_apps, :country, :string
end
end
remove_column :table_name, :column_name
rails g migration Remove..From.. col1:type col2:type col3:type
#Exemple :
rails g migration RemoveCountryFromSampleApps country:string