public function on($firstColumn, $operator, $secondColumn, $boolean = 'and', $where = false) {
		
		if ($where)
			$this->bindings[] = $secondColumn;
		
		if ($where && ($operator === 'in' || $operator === 'not in') && is_array($secondColumn)) {
			$secondColumn = count($secondColumn);
		}
		
		$this->clauses[] = compact('firstColumn', 'operator', 'secondColumn', 'boolean', 'where');
		
		return $this;
	}