function getTagsByBook( $blog_id, $tag_group ) {

		/** @var $wpdb \wpdb */
		global $wpdb;

		$sql = "SELECT DISTINCT {$this->dbTagsTable}.id, {$this->dbTagsTable}.tag FROM {$this->dbTagsTable}
 				INNER JOIN {$this->dbLinkTable} ON {$this->dbLinkTable}.tags_id = {$this->dbTagsTable}.id
 				INNER JOIN {$this->dbTable} ON {$this->dbTable}.users_id = {$this->dbLinkTable}.users_id AND {$this->dbTable}.blogs_id = {$this->dbLinkTable}.blogs_id
 				WHERE {$this->dbLinkTable}.tags_group = %d AND {$this->dbLinkTable}.users_id = %d AND {$this->dbLinkTable}.blogs_id = %d
 				ORDER BY {$this->dbTagsTable}.tag ASC ";

		return $wpdb->get_results( $wpdb->prepare( $sql, $tag_group, $this->userId, $blog_id ), ARRAY_A ); // @codingStandardsIgnoreLine
	}