Various Column Operations in Rails

$ rails g migration change_column_name_to_table_name
ex) rails g migration change_age_to_users

class ChangeColumnToUsers < ActiveRecord::Migration
 # Changes to be made
def up
  change_column :users, :age, :integer, null: false, default: 0
end
 # Revert changes
 def down
  change_column :users, :age, :integer, null: false
end
end

$ rails g migration remove_column_name_from_table_name column_name
ex) rails g migration remove_age_from_users age

$ rails g migration add_column_name_to_table_name column_name:data_type
ex) rails g migration add_age_to_users age:integer

$ rake db:migrate