Answers for "rails db migrate"

activerecord add column

class AddPartNumberToProducts < ActiveRecord::Migration[6.0]
  def change
    add_column :products, :part_number, :string
  end
end

rails g migration add columns

$ rails generate migration AddDetailsToProducts part_number:string price:decimal

using SQL in rails migration

def change
  execute <<-SQL
    UPDATE table1
    SET column1 = "value"
  SQL
end

rials db down

bin/rails db:migrate:down VERSION=YYYYMMDDHHMMSS