Convert the string "NULL" into a proper NULL across an entire database.

nullify.rb

require 'rubygems'
require 'mysql'

@database = {
  'host' => '',
  'user' => '',
  'password' => '',
  'name' => ''
}

def sql
  # start your engines
  @@mysql = Mysql.new(@database['host'], @database['user'], @database['password'], @database['name'])
end

# update tables
tables = sql.list_tables

# update columns
tables.each do |table|
  columns = sql.query("SHOW FULL COLUMNS FROM `#{table}`;")
  columns.each_hash do |column|  
    sql.query("UPDATE `#{table}` SET #{column['Field']} = null WHERE #{column['Field']} = 'NULL';")
    puts "Column #{table}.#{column['Field']} was nullified."
  end
end

# shut down
sql.close