# for rails 2
if ENV.include?('RAILS_ENV')
  if !Object.const_defined?('RAILS_DEFAULT_LOGGER')
    require 'logger'
    Object.const_set('RAILS_DEFAULT_LOGGER', Logger.new(STDOUT))
  end

  def sql(query)
    ActiveRecord::Base.connection.select_all(query)
  end
# for rails 3
elsif defined?(Rails) && !Rails.env.nil?
  if Rails.logger
    Rails.logger = Logger.new(STDOUT)
    ActiveRecord::Base.logger = Rails.logger
  end
end

# execute this line in rails console
ActiveRecord::Base.logger = Logger.new(STDOUT)

# or paste this in ~/.irbrc
# works for both Rails2 and Rails3
require 'logger'
if ENV.include?('RAILS_ENV') && !Object.const_defined?('RAILS_DEFAULT_LOGGER')
   Object.const_set('RAILS_DEFAULT_LOGGER', Logger.new(STDOUT))
else
   ActiveRecord::Base.logger = Logger.new(STDOUT)
end

# just execute this line
ActiveRecord::Base.logger = Logger.new(STDOUT)

SQL log in Rails console

sql, rails, log

Rails