Parent child mysql

Question

Say I have a table like this:

=================================
| ID |  Parent_ID | Page_Name   |
=================================
| 1  |  NULL      |  Home       |
| 2  |  NULL      |  Services   |
| 3  |  2         |  Baking     |
| 4  |  3         |  Cakes      |
| 5  |  3         |  Bread      |
| 6  |  5         |  Flat Bread |
---------------------------------

How can I go about actually ordering the results in this format? I.e. Ordered by the Parent -> Child -> Sub Child, on the basis I would only ever require say a maximum of 5 levels? I have looked into the "Nested Set Model" but it seems too complex for my requirements. What I am unsure about is really understanding a SQL query I can use to display my results like above, or in this situation should I be using a server side language like PHP to do this for me?

Answer 1

EDIT

working sample addressing Gordons note

Query calculate node path as you have fixed maximum tree depth, and order by it.

SQL Fiddle

MySQL 5.5.30 Schema Setup:

create table mytable(id int, parent_id int, name varchar(100));

insert mytable(id, parent_id, name)
values (1, null, 'Home'),
(2, null, 'Services'),
(3, 2, 'Baking'),
(4, 3, 'Cakes'),
(5, 3, 'Bread'),
(6, 5, 'Flat Bread'),
(7, 1, 'Something');

Query 1:

select t0.*,
  concat(
      case coalesce(t4.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t4.Parent_ID as char), '\\')
      end,
      case coalesce(t3.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t3.Parent_ID as char), '\\')
      end,
      case coalesce(t2.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t2.Parent_ID as char), '\\')
      end,
      case coalesce(t1.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t1.Parent_ID as char), '\\')
      end,
      case coalesce(t0.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t0.Parent_ID as char), '\\')
      end,
      cast(t0.id as char)
    ) as path
from mytable t0 
    left join mytable t1 on t0.Parent_ID = t1.Id
    left join mytable t2 on t1.Parent_ID = t2.Id
    left join mytable t3 on t2.Parent_ID = t3.Id
    left join mytable t4 on t3.Parent_ID = t4.Id
order by 
  concat(
      case coalesce(t4.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t4.Parent_ID as char), '\\')
      end,
      case coalesce(t3.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t3.Parent_ID as char), '\\')
      end,
      case coalesce(t2.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t2.Parent_ID as char), '\\')
      end,
      case coalesce(t1.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t1.Parent_ID as char), '\\')
      end,
      case coalesce(t0.Parent_ID, 0) 
        when 0 then ''
        else concat(cast(t0.Parent_ID as char), '\\')
      end,
      cast(t0.id as char)
    )

Results:

| ID | PARENT_ID |       NAME |    PATH |
-----------------------------------------
|  1 |    (null) |       Home |       1 |
|  7 |         1 |  Something |     1\7 |
|  2 |    (null) |   Services |       2 |
|  3 |         2 |     Baking |     2\3 |
|  4 |         3 |      Cakes |   2\3\4 |
|  5 |         3 |      Bread |   2\3\5 |
|  6 |         5 | Flat Bread | 2\3\5\6 |