Question

I need to develop a good table structure for creating a sortable multilevel list using SQL Server Database.

Here is an example of the way I develop sortable multilevel lists:

A
├──B
|  ├──E
|  ├──F
|  ├──O
|
├──C
|  ├──M
|

My table structure:

ID   Title   Parent   Sort
---------------------------
1    A       Null     0
2    B       A        0
3    E       B        0
4    F       B        1
5    O       B        2
6    C       A        1
7    M       C        0

Now, would you mind telling me the best way of developing such lists?
Thank you very much indeed.

Answer 1

Just go with your outlined structure. SQL Server supports recursive queries via CTEs, something like this will do the trick for you:

WITH tree AS (
  SELECT id, name, parent,
         0 AS level,
         CAST(sort AS varchar(90)) AS path,
         CAST(name AS varchar(90)) AS fullname
    FROM test WHERE parent IS NULL
  UNION ALL
  SELECT t.id, t.name, t.parent, tree.level + 1,
         CAST(tree.path + '.' + CAST(t.sort AS varchar) AS varchar(90)),
         CAST(tree.fullname + '.' + t.name AS varchar(90))
    FROM test t
    JOIN tree ON t.parent = tree.name
)
SELECT id, name, parent, level, path, fullname FROM tree
ORDER BY path;

I’m building some extra informative fields here:

• level, indicating depth of the node from the root;
• path, which is built based on your sort field and is used to sort the tree properly;
• fullname — just a nice view on the full node name.

You can try this query here.

Please, consider the size of your data — for huge data structures you might want to push predicates into the inner query for better performance.