How to fill in the “holes” in auto-increment fields?

Question

I\'ve read some posts about this but none cover this issue.

I guess its not possible, but I\'ll ask anyway.

I have a table with more than 50.000 registers. I

Answer 1

As others have said, it doesn't matter, and if it does then something is wrong in your database design. But personally I just like them to be in order anyway!

Here is some SQL that will recreate your IDs in the same order, but without the gaps.

It is done first in a temp_id field (which you will need to create), so you can see that it is all good before overwriting your old IDs. Replace Tbl and id as appropriate.

SELECT @i:=0;
UPDATE Tbl
JOIN
(
    SELECT id
    FROM Tbl
    ORDER BY id
) t2
ON Tbl.id = t2.id
SET temp_id = @i:=@i+1;

You will now have a temp_id field with all of your shiny new IDs. You can make them live by simply:

UPDATE Tbl SET id = temp_id;

And then dropping your temp_id column.

I must admit I'm not quite sure why it works, since I would have expected the engine to complain about duplicate IDs, but it didn't when I ran it.