How to reorder a primary key?

Question

I have a table of 5700 records. The primary key is an integer. Now I noticed that some values are missing. Like this:

100 data
101 data 
102 data
104 data

103 is missing. How I can update all the rows so that the order becomes correct (104 becomes 103 in my example) in one SQL command?

Answer 1

Try this:

SET @var:=0;
UPDATE `table` SET `id`=(@var:=@var+1);
ALTER TABLE `table` AUTO_INCREMENT=1; 

Answer 2

There is no point in doing this.

IDs from deleted records are not re-used on purpose - to make sure that references from other tables to previously deleted records don't suddenly point to the wrong record, for example. It is not a good idea to try to change this.

If you want a numbered list that has no holes, create a second int column that you re-order in your client program whenever necessary (i.e. when a record is deleted).