diff --git a/files/default/sql/ddl/updates/3.4.0.sql b/files/default/sql/ddl/updates/3.4.0.sql
index 77ca56e38..83124bfb8 100644
--- a/files/default/sql/ddl/updates/3.4.0.sql
+++ b/files/default/sql/ddl/updates/3.4.0.sql
@@ -158,6 +158,18 @@ ALTER TABLE `hopsworks`.`feature_group` ADD COLUMN `topic_name` VARCHAR(255) DEF
 ALTER TABLE `hopsworks`.`project` ADD COLUMN `topic_name` VARCHAR(255) DEFAULT NULL;
 
 SET SQL_SAFE_UPDATES = 0;
+-- deletes unused topics (fg was deleted)
+DELETE
+FROM `hopsworks`.`project_topics`
+WHERE REGEXP_SUBSTR(`topic_name`, "^([0-9]+)_([0-9]+)_(.+)_([0-9]+)(_onlinefs|$)")
+  AND REGEXP_REPLACE(`topic_name`, "^([0-9]+)_([0-9]+)_(.+)_([0-9]+)(_onlinefs|$)", '$2') NOT IN (SELECT `feature_group`.`id` FROM `feature_group`);
+
+-- deletes unused subjects (fg was deleted)
+DELETE
+FROM `hopsworks`.`subjects`
+WHERE REGEXP_SUBSTR(`subject`, "^([0-9]+)_([0-9]+)_(.+)_([0-9]+)(_onlinefs|$)")
+  AND REGEXP_REPLACE(`subject`, "^([0-9]+)_([0-9]+)_(.+)_([0-9]+)(_onlinefs|$)", '$2') NOT IN (SELECT `feature_group`.`id` FROM `feature_group`);
+
 UPDATE `hopsworks`.`subjects`
 SET `subject` = REGEXP_REPLACE(`subject`, "^([0-9]+)_([0-9]+)_(.+)_([0-9]+)(_onlinefs|$)",'$3_$4')
 WHERE REGEXP_SUBSTR(`subject`, "^([0-9]+)_([0-9]+)_(.+)_([0-9]+)(_onlinefs|$)");