========== tester.rb
require 'rubygems'
require 'sequel'
require 'logger'

Sequel.connect(:database => 'sequel_tester', :adapter => 'mysql', :host => 'localhost', :username => 'root', :password => '', :logger => Logger.new('sequel.log'))

class Animal < Sequel::Model
  set_schema do
    primary_key :id
    String :name, :unique => true
  end

  def self.multi_insert_ignore(*args)
    def dataset.multi_insert_sql(columns,values)
      sql = super(columns,values)
      sql[0].gsub!(/^INSERT/,'INSERT IGNORE')
    end
    multi_insert(*args)
  end

  def self.multi_insert_update(*args)
    def dataset.multi_insert_sql(columns,values)
      sql = super(columns,values)
      dup = columns.map {|column| "#{column}=VALUES(#{column})"}.join(', ')
      sql[0] << " ON DUPLICATE KEY UPDATE #{dup}"
    end
    multi_insert(*args)
  end
end

Animal.create_table unless Animal.table_exists?
Animal.delete_all

@columns = [:name,:kind]

@values1 = [
  ['sally','monkey'],
  ['bob','bird'],
  ['john','monkey'],
  ['mark','elephant'],
  ['fred','bird']
  ]

@values2 = [
  ['sally','monkey2'],
  ['bob','bird2'],
  ['john','monkey2'],
  ['mark','elephant2'],
  ['fred','bird2']
  ]

def ignore
  Animal.multi_insert_ignore(@columns,@values1, :slice => 2)
end

def update
  Animal.multi_insert_update(@columns,@values2, :slice => 2)
end

def results
  puts "#{Animal.first.name} : #{Animal.first.kind}"
end

ignore
results
ignore
results
update
results
update
results

========== output from command line
$ irb -r tester.rb
sally : monkey
sally : monkey
sally : monkey2
sally : monkey2


========== sequel.log

# Logfile created on Tue Mar 24 14:46:17 -0400 2009 by /
I, [2009-03-24T14:46:17.736067 #68545]  INFO -- : DESCRIBE `animals`
I, [2009-03-24T14:46:17.740144 #68545]  INFO -- : DELETE FROM `animals`
I, [2009-03-24T14:46:17.740815 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.740995 #68545]  INFO -- : INSERT IGNORE INTO `animals` (`name`, `kind`) VALUES ('sally', 'monkey'), ('bob', 'bird')
I, [2009-03-24T14:46:17.741872 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.742173 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.742338 #68545]  INFO -- : INSERT IGNORE INTO `animals` (`name`, `kind`) VALUES ('john', 'monkey'), ('mark', 'elephant')
I, [2009-03-24T14:46:17.743008 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.743265 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.743420 #68545]  INFO -- : INSERT IGNORE INTO `animals` (`name`, `kind`) VALUES ('fred', 'bird')
I, [2009-03-24T14:46:17.743852 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.744188 #68545]  INFO -- : SELECT * FROM `animals` LIMIT 1
I, [2009-03-24T14:46:17.745010 #68545]  INFO -- : SELECT * FROM `animals` LIMIT 1
I, [2009-03-24T14:46:17.745815 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.746049 #68545]  INFO -- : INSERT IGNORE INTO `animals` (`name`, `kind`) VALUES ('sally', 'monkey'), ('bob', 'bird')
I, [2009-03-24T14:46:17.746801 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.747110 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.747277 #68545]  INFO -- : INSERT IGNORE INTO `animals` (`name`, `kind`) VALUES ('john', 'monkey'), ('mark', 'elephant')
I, [2009-03-24T14:46:17.747903 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.748162 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.748316 #68545]  INFO -- : INSERT IGNORE INTO `animals` (`name`, `kind`) VALUES ('fred', 'bird')
I, [2009-03-24T14:46:17.748784 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.749116 #68545]  INFO -- : SELECT * FROM `animals` LIMIT 1
I, [2009-03-24T14:46:17.749740 #68545]  INFO -- : SELECT * FROM `animals` LIMIT 1
I, [2009-03-24T14:46:17.750453 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.750643 #68545]  INFO -- : INSERT INTO `animals` (`name`, `kind`) VALUES ('sally', 'monkey2'), ('bob', 'bird2') ON DUPLICATE KEY UPDATE name=VALUES(name), kind=VALUES(kind)
I, [2009-03-24T14:46:17.751519 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.751817 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.751982 #68545]  INFO -- : INSERT INTO `animals` (`name`, `kind`) VALUES ('john', 'monkey2'), ('mark', 'elephant2') ON DUPLICATE KEY UPDATE name=VALUES(name), kind=VALUES(kind)
I, [2009-03-24T14:46:17.752730 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.752994 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.753157 #68545]  INFO -- : INSERT INTO `animals` (`name`, `kind`) VALUES ('fred', 'bird2') ON DUPLICATE KEY UPDATE name=VALUES(name), kind=VALUES(kind)
I, [2009-03-24T14:46:17.753703 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.754027 #68545]  INFO -- : SELECT * FROM `animals` LIMIT 1
I, [2009-03-24T14:46:17.754807 #68545]  INFO -- : SELECT * FROM `animals` LIMIT 1
I, [2009-03-24T14:46:17.755523 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.755710 #68545]  INFO -- : INSERT INTO `animals` (`name`, `kind`) VALUES ('sally', 'monkey2'), ('bob', 'bird2') ON DUPLICATE KEY UPDATE name=VALUES(name), kind=VALUES(kind)
I, [2009-03-24T14:46:17.756490 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.756786 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.756995 #68545]  INFO -- : INSERT INTO `animals` (`name`, `kind`) VALUES ('john', 'monkey2'), ('mark', 'elephant2') ON DUPLICATE KEY UPDATE name=VALUES(name), kind=VALUES(kind)
I, [2009-03-24T14:46:17.757744 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.758013 #68545]  INFO -- : BEGIN
I, [2009-03-24T14:46:17.758179 #68545]  INFO -- : INSERT INTO `animals` (`name`, `kind`) VALUES ('fred', 'bird2') ON DUPLICATE KEY UPDATE name=VALUES(name), kind=VALUES(kind)
I, [2009-03-24T14:46:17.758630 #68545]  INFO -- : COMMIT
I, [2009-03-24T14:46:17.758954 #68545]  INFO -- : SELECT * FROM `animals` LIMIT 1
I, [2009-03-24T14:46:17.759592 #68545]  INFO -- : SELECT * FROM `animals` LIMIT 1