Question

I have a table of categories. Each category can either be a root level category (parent is NULL), or have a parent which is a root level category. There can’t be more than one level of nesting.

I have the following table structure:

Categories Table Structure http://img16.imageshack.us/img16/8569/categoriesi.png

Is there any way I could use a query which produced the following output:

Free Stuff
Hardware
Movies
CatA
CatB
CatC
Software
Apples
CatD
CatE

So the results are ordered by top level category, then after each top level category, subcategories of that category are listed?

It’s not really ordering by Parent or Name, but a combo of the two. I’m using SQL Server.

Answer 1

Ok, here we go :

with foo as
(
select 1 as id, null as parent, 'CatA' as cat from dual
union select 2, null, 'CatB' from dual
union select 3, null, 'CatC' from dual
union select 4, 1, 'SubCatA_1' from dual
union select 5, 1, 'SubCatA_2' from dual
union select 6, 2, 'SubCatB_1' from dual
union select 7, 2, 'SubCatB_2' from dual
)
select child.cat
from foo parent right outer join foo child on parent.id = child.parent
order by case when parent.id is not null then parent.cat else child.cat end,
         case when parent.id is not null then 1 else 0 end

Result :

CatA
SubCatA_1
SubCatA_2
CatB
SubCatB_1
SubCatB_2
CatC

Edit – Solution change inspire from van’s order by ! Much simpler that way.