public function toSql() {
		
		if ($this->type == 'insert') {
			return $this->grammar->compileInsert($this);
		} else if ($this->type == 'update') {
			return $this->grammar->compileUpdate($this);
		} else if ($this->type == 'delete') {
			return $this->grammar->compileDelete($this);
		} else {
			return $this->grammar->compileSelect($this);
		}
		
	}