AssignmentsReportsGenerator::addAdditionalFields( $strFields )

	public function addAdditionalFields($strFields)
	{
		global $wpdb;
		$quizPostType = learndash_get_post_type_slug('quiz');

		$fields = "
			users.ID as user_id,
			users.display_name as user_display_name,
			users.user_email as user_email,
			{$wpdb->posts}.ID as assignment_id,
			{$wpdb->posts}.post_title as assignment_title,
			{$wpdb->posts}.post_date_gmt as assignment_post_date,
			{$wpdb->posts}.post_modified_gmt as assignment_modify_date,
			(
				SELECT meta_value
				FROM {$wpdb->postmeta} as course_meta
				WHERE course_meta.post_id = {$wpdb->posts}.ID
				AND course_meta.meta_key = 'course_id'
			) as activity_course_id,
			(
				SELECT post_title
				FROM {$wpdb->posts} as courses
				WHERE activity_course_id = courses.ID
			) as activity_course_title
		";

		return $fields;
	}