As I and others in this thread have pointed out, an UPDATE statement with no WHERE clause updates all rows in the database. If you only wnat to update some rows, you need a WHERE clause. After all this you have never explained what you actually want to do. In which situation do you want to set the ID to 0? to 50? ... And it's very unclear why on earth you are mucking with the IDs anyway. There's no point in discussing the details further unless you can explain what you want to accomplish.

update I'm sorry if I'm being harsh. There's no sin in you not understanding this. But if you want us to help, *please* tell us what you are trying to accomplish.