diff --git a/manual/administration/clean_database.md b/manual/administration/clean_database.md
index cd463243..4c963c2b 100644
--- a/manual/administration/clean_database.md
+++ b/manual/administration/clean_database.md
@@ -29,10 +29,9 @@ Use the following command to clear the activity records:
 ```
 use seahub_db;
 DELETE FROM Activity WHERE to_days(now()) - to_days(timestamp) > 90;
+DELETE FROM UserActivity WHERE to_days(now()) - to_days(timestamp) > 90;
 ```
 
-The corresponding items in UserActivity will deleted automatically by MariaDB when the foreign keys in Activity table are deleted.
-
 ### Login
 
 Use the following command to clean the login records: