从表中删除另一个表中不存在列的行

I have this SQL query that deletes a user's preferences from USERPREF table if they have not logged in for 30 days (last login date located in MOMUSER table), however, it does not verify that the user still exists in MOMUSER. How can I change this so that if USERPREF.CUSER does not exist in MOMUSER.CODE that the USERPREF row is also deleted in that situation since they will not have a last login date?I have this SQL query that deletes a user's pre