protected function _composeUpdateQuery(SQL $SQL){

		$condition = parent::compose($SQL);

		$query_pre = "UPDATE `$this->_table` SET ";
		$query_post = " WHERE $condition";

		$fields = [];

		if(empty($this->_fields)){

			throw new QueryBuilderException(
				'No fields specified for SQL query'
			);
		}

		foreach($this->_fields as $field => $value){

			$fields[] = "$field = " . $this->_prepareValue($value, $SQL);
		}

		return $query_pre . implode(', ', $fields) . $query_post;
	}