Listing the category and subcategory from single table

You table structure

create table categories
( id       integer     not null  primary key
, name     varchar(37) not null
, parentid integer     null
, foreign key parentid_fk (parentid)
      references categories (id)
);

Your Sql

select root.name  as root_name
     , down1.name as down1_name
     , down2.name as down2_name
     , down3.name as down3_name
  from categories as root
left outer
  join categories as down1
    on down1.parentid = root.id
left outer
  join categories as down2
    on down2.parentid = down1.id
left outer
  join categories as down3
    on down3.parentid = down2.id
 where root.parentid is null
order
    by root_name
     , down1_name
     , down2_name
     , down3_name