Need some help with a SQL query (SQL Server 2005) to transform this data

Question

Here's a simplistic look at the table I have

Category

• CategoryId
• CategoryName
• ParentCategoryId

As you can see, the catalog table is a self referencing table, so recursing it is possible by starting at 0, which is the fake "root" category (could just as well be null, but it's not).

Sample Data:

1, Apples, 0
5, Yummy, 1
10, Really Yummy, 5
15, Yucky, 0
18, Some Sub Cat, 15
20, Some Deep Sub Cat, 18
25, Some Deep Sub Cat 2, 18

The deepest any category hierarchy can be is 4 deep, and I'm trying to get an output that looks like this:

CatId, [up to 4 deep of category names on the hierarchy in separate columns, or null if none]
1, Apples, NULL, NULL, NULL
5, Apples, Yummy, NULL, NULL
10, Apples, Yummy, Really Yummy, NULL
15, Apples, Yucky, NULL, NULL
18, Apples, Yucky, Some Sub Cat, NULL
20, Apples, Yucky, Some Sub Cat, Some Deep Sub Cat
25, Apples, Yucky, Some Sub Cat, Some Deep Sub Cat 2

This SQL is close, but it generates it backwards, left justified

select c1.categoryid, c1.name, c2.name, c3.name, c4.name
from category c1
    left outer join category c2
     on c1.parentcategoryid = c2.categoryid
    left outer join category c3
     on c2.parentcategoryid = c3.categoryid
    left outer join category c4
     on c3.parentcategoryid = c4.categoryid

Any SQL geniuses have some good ideas?

Answer 1

select c1.CategoryId as id,
       c1.CategoryName as n1,
       c2.CategoryName as n2,
       c3.CategoryName as n3,
       c4.CategoryName as n4
from            Category c1
left outer join Category c2 on c2.ParentCategoryId = c1.CategoryId
left outer join Category c3 on c3.ParentCategoryId = c2.CategoryId
left outer join Category c4 on c4.ParentCategoryId = c3.CategoryId
where c1.parentcategoryid = 0;

(per your edit: you've just got ParentCategoryId and CategoryID flipped in the joins.)