Question

I’m doing a test web shop that has sections within sections. There can be an unlimited number of levels so I have just one table Section.

The table has the following columns:

SectionID, SectionTitle, SectionLevel, ParentID, PageOrder

SectionLevel: 1 being topmost (no parent)

PageOrder: Within it’s parent group, which order it should go in.

And for test data :

SectionID  SectionTitle  SectionLevel  ParentID  PageOrder
---------  ------------  ------------  --------  ---------
2          Ladies        1             0         2
3          Mens          1             0         3
4          Jewellery     2             2         1 
5          Clothing      2             2         2
6          Clothing      2             3         1 
7          Accessories   2             3         2

I want to return this data in one table so that the first top level section is first, and then all of it’s children’s sections are next, and then the second top level section etc.

I’ve had a play around with it but can’t get to come out right. I think that it should be possible to do it if I redesigned the table but can’t think how.

The data should come back in the following order:

SectionID  SectionTitle  SectionLevel  ParentID  PageOrder
---------  ------------  ------------  --------  ---------
2          Ladies        1             0         2
4          Jewellery     2             2         1 
5          Clothing      2             2         2
3          Mens          1             0         3
6          Clothing      2             3         1 
7          Accessories   2             3         2

Answer 1

This is deliberately slightly niaive to make it easier on my fingers. It can be tuned if necessary to allow more nodes in the tree to be accomodated.

DECLARE
  @maxPageOrder INT,
  @maxLevel     INT,
  @multiplier   INT

SELECT
  @maxPageOrder  = MAX(PageOrder) + 1,
  @maxLevel      = MAX(SectionLevel)
FROM
  Section

SELECT
  @multiplier = POWER(@maxPageOrder, @maxLevel - 1)    
;

WITH
  recursed_tree
AS
(
  SELECT
    SectionID                      AS SectionID,
    PageOrder * @multiplier        AS finalOrder,
    @multiplier / @maxPageOrder    AS multiplier
  FROM
    Section
  WHERE
    ParentID = 0

  UNION ALL

  SELECT
    child.SectionID,
    parent.finalOrder + child.PageOrder * parent.multiplier,
    parent.multiplier / @maxPageOrder
  FROM
    recursed_tree  AS parent
  INNER JOIN
    Section        AS child
      ON child.ParentID = parent.SectionID
)

SELECT
  Section.*
FROM
  Section
INNER JOIN
  recursed_tree
    ON Section.SectionID = recursed_tree.SectionID
ORDER BY
  recursed_tree.finalOrder

Note: This assumes all page orders start from 1, rather than 0.