php mysql problem

Just say I have a db CREATE TABLE mytable ( id int(4) NOT NULL auto_increment, fileName varchar(50) NOT NULL default '', PRIMARY KEY (id) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=7 ; when I add items they go id 1,2,3 etc. Whn I delete them gaps appear. 1, 3, 7. I need to know (a) when items are removed how can I sort the database to all the gaps are take out 1, 3, 7 becomes 1,2,3 (b) allow the ids to be changed so the items can change position in the list. If I change id 3 to id 1 then everything else shifts down. If anyone has seen the amazon dvd rental list where you can swap dvd to the top of the list and delete this is what I am trying to achive with php/mysql.