dsl_sql.rb

class Query 
  def initialize(&block)
    instance_eval(&block)
  end

  def select(select); @select = select; end
  def from  (from  ); @from   = from  ; end
  
  def where(op, where)
    (@where ||= []) << [ op, where]
  end
  
  def to_s
    "SELECT #{@select} FROM #{@from} WHERE ".tap { |o|
      @where.each_with_index { |where, i|
        o << "#{where[1].keys.first} #{Query.get_op where[0]} '#{where[1].values.first}'"
        o << " && " if @where.length > (i + 1)
      }
    }
  end
  
  def Query.get_op(op)
    { :equals => ?=, :greater => ?> }[op]
  end
    
end


query = Query.new do
  select :user
    from :nerdz
      where :equals,  :username => 'Robertof'
      where :greater, :age      => 12
end

puts query