Question

I have a ‘Categories’ table. Each row has a ‘CategoryId’ (required), and a ‘ParentCategoryId’ (not required). This allows for a Parent–>Child relationships between categories.

What I’m trying to do is select all categories, but if a parent–>child relationship exists, select only the parent.

Here’s what I’m currently trying, but it’s taking forever, and is just flat wrong. Disclaimer, SQL is NOT my strong suit!

declare @ProjectId int
set @ProjectId = 1

declare @catid int
declare @catname nvarchar(100)
declare @catprojid int
declare @catparentid int
declare @sortorder int

declare db_cursor cursor for
select categoryid,categoryname,projectid,parentcategoryid,sortorder from dbo.ProjectCategories
where ProjectId = @ProjectId

open db_cursor
fetch NEXT from db_cursor into @catid,@catname,@catprojid,@catparentid,@sortorder

while @@FETCH_STATUS = 0
begin
    if @catparentid != null select * from dbo.ProjectCategories where CategoryId = @catparentid
    else select @catid,@catname,@catprojid,@catparentid,@sortorder
end

close db_cursor
deallocate db_cursor
go

Answer 1

The following select retrieves all the Categories that are parents to at least one other Category:

declare @ProjectId int
set @ProjectId = 1

select distinct
    parent.categoryid, 
    parent.categoryname, 
    parent.projectid, 
    parent.parentcategoryid, 
    parent.sortorder 
from dbo.ProjectCategories parent
join dbo.ProjectCategories child on child.ParentCategoryId = parent.CategoryId
where parent.ProjectId = @ProjectId