code: public function on($column1, $op, $column2)
  	{
  		if ($this->active_join === null)
  		{
  			throw new \Peyote\Exception("You need to start a join before calling \Peyote\Join::on()");
  		}
  
  		list($table, $type) = $this->active_join;
  		$this->active_join = null;
  		$this->joins[] = array("ON", $table, $type, $column1, $op, $column2);
  		return $this;
  	}
docs: Creates an ON join.
  
  @throws \Peyote\Exception
  
  @param  string $column1  The column from the first table
  @param  string $op       The operator
  @param  string $column2  The column from the second table
  @return \Peyote\Join