week_nr_comparison.rb

require 'active_record'
require 'mysql2'

ActiveRecord::Base.establish_connection(adapter: :mysql2, username: 'root')

(Date.new(2000, 01, 01)..Date.new(2020, 12, 31)).each do |date|
  mysql_week = ActiveRecord::Base.connection.execute("SELECT WEEK('#{date.to_s}', 3)").first.first
  ruby_week = date.cweek
  unless mysql_week == ruby_week
    puts "Week numbers differ for date #{date} (mysql: #{mysql_week}, ruby: #{ruby_week})"
  end
end