EssaysReportsGenerator::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 essay_id,
			{$wpdb->posts}.post_title as essay_title,
			{$wpdb->posts}.post_date_gmt as essay_post_date,
			{$wpdb->posts}.post_modified_gmt as essay_modify_date,
			{$wpdb->posts}.comment_count as essay_comment_count,
			(
				SELECT meta_value
				FROM {$wpdb->postmeta} as pro_quiz_meta
				WHERE pro_quiz_meta.post_id = {$wpdb->posts}.ID
				AND pro_quiz_meta.meta_key = 'quiz_pro_id'
			) as pro_quiz_id,
			(
				SELECT post_id
				FROM {$wpdb->postmeta} as quiz_meta
				INNER JOIN {$wpdb->posts} as qm_posts ON qm_posts.ID = quiz_meta.post_id
				WHERE quiz_meta.meta_key = 'quiz_pro_id'
				AND quiz_meta.meta_value = pro_quiz_id
				and qm_posts.post_type = '{$quizPostType}'
			) as quiz_id,
			(
				SELECT quizes.post_title
				FROM {$wpdb->posts} as quizes
				WHERE quiz_id = quizes.ID
			) as quiz_title,
			(
				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 {$wpdb->posts} as courses
				WHERE activity_course_id = courses.ID
			) as activity_course_title,
			IF ({$wpdb->posts}.post_status = 'graded', {$wpdb->posts}.post_modified, 0) as activity_completed
		";

		return $fields;
	}