Need help for stange behaveour

[Rosen Ralev]

Hi :) I need help on the following problem.
I have the following table,

id name parent
1 1dno 5
2 2ve 0
5 3i 2
4 4i 1

And execute:

SELECT * , @a := id
FROM `test`
WHERE parent = @a
OR parent =0;

And I get for result:

id name parent @a := id
2 2ve 0 2
5 3i 2 5

So my question is, why I get only two results. I assumed that it would return the entire table starting with the row which parent is zero and then the next row will be with parent = 2 and then parent=5 and so on. This way I wanted to order the rows following the parent dependency.
I am not sure if this is the right way to do it, but I am puzzled by the result this query gives.
I would appreciate if some body explains to me why do I get this result.
I am testing it on MySQL 5.0.32

If there is an other way to achieve the order i desire, please tell so :)

Thank you in advance :)