I am not sure if I understand you correctly. In order to assist you best please elaborate a bit more on your scenario:
Which database do you mean? If you want to clear the Scheduling database you should go to Results tab > Scheduling Server ribbon > Manage Results window and do it from there. This will completely delete the run results from the Scheduling database.
We really don't recommend manually deleting results directly from the database, because this could lead to unexpected behavior.
If you want to delete all results you can also create a new datebase and delete the old one.
If I am missing something please give us more detailed information.
Hope to hear from you soon.
the Telerik team