SQL UPDATE with IGNORE keyword http://dev.mysql.com/doc/refman/5.0/en/update.html

update_ignore.rb

module UpdateIgnore
  def update_ignore(updates, conditions)
    set = updates.map{|k,v| "#{connection.quote_column_name(k)} = #{connection.quote v}" }.join(', ')
    connection.update "UPDATE IGNORE #{quoted_table_name} SET #{set} WHERE #{self.where(conditions).where_clauses.join('AND')}"
  end
end