如何在表中存在时从表中进行选择

When a lecture (a row in 'lectures' table) is deleted, it is moved into the 'lectures_deleted' table. This acts as a sort of back-up. In this case, I need to be able to call from both of these tables, so I would like to get the data from the 'lectures' table, though if it does not exist here, I would then like to get it instead from the 'lectures_deleted' table.When a lecture (a row in 'lectures' table) is d