SQL order by grouping children of the same parent (one generation)

I am assuming there is only a generation, so I want to order the result from a db table with (id,parent_id) structure implementing the parent-child internal relationship, ie:

Table name: **catogories**
id	parent_id	name
int	int	varchar(100)

So, I found some hint here, and here, but actually I did wrote my solution first using IF in SQL:

SELECT c.*, IF(c.parent_id = 0, c.id*1000, c.parent_id*1000+c.id) as sorter FROM categories as c ORDER BY sorter

And for one generation structure, it works. Results are something like:

results
id	parent_id	name	sorter
1	0	Fruits	1001
3	1	Banana	1003
2	0	Vegetables	2002

That look simple enough

Note on image source: flickr vivariphotography, CC, commercial use allowed, link