SQL Server: CTE tree with priority - sql

Question

I have some troubles how to build a query for a recursive parent-child tree in SQL Server.
I have found some common table expression but i have to consider another parameter (the priority in each level) that i have not found from a search over the internet, so the structure of my table is like this
id - parentid - proprity
For example if i have this data:
1 - NULL - 2
2 - NULL - 1
3 - 2 - 2
4 - 3 - 1
5 - 2 - 0
6 - 1 - 0
7 - 2 - 3
The query must return this at right order:
-2
--5
--3
---4
--7
-1
--6
Also this list is orderable so if any order is change I have to reset the priority at right place. Anyone has already a solution for this case with queries in SQL Server?
Thanks in advance

Answer 1

This will give you the order that you need. Personally, I'd try to do that ordering in the display layer, but this will do it in SQL.
This relies on single-digit priority values. If those might be larger then you'll need to prepend leading 0s to the priorities, like: RIGHT('0' + priority, 2).
The query just builds a string of the priorities at each point so that you can then order off of it.
;WITH Hierarchy_CTE AS
(
SELECT
id,
parent_id,
CAST([priority] AS VARCHAR(100)) AS priority_string,
id AS base,
1 AS lvl
FROM
My_Table
WHERE
parent_id IS NULL
UNION ALL
SELECT
MT.id,
MT.parent_id,
CAST(H.priority_string + CAST(MT.priority AS VARCHAR(20)) AS VARCHAR(100)),
H.base,
H.lvl + 1
FROM
Hierarchy_CTE H
INNER JOIN My_Table MT ON MT.parent_id = H.id
)
SELECT
id,
base,
lvl
FROM
Hierarchy_CTE
ORDER BY
priority_string

Answer 2

It seems that this solution is working (taken from Tom H answer):
;WITH Hierarchy_CTE AS
(
SELECT
id,
parent_id,
CAST(REPLICATE('0', 10 - LEN(CAST([Order] AS VARCHAR))) + CAST([Order] AS VARCHAR) + '.' +
REPLICATE('0', 10 - LEN(CAST(MerchantCategoryId AS VARCHAR))) + CAST(MerchantCategoryId AS VARCHAR) AS VARCHAR(4000)) AS priority_string,
id AS base,
1 AS lvl
FROM
My_Table
WHERE
parent_id IS NULL
UNION ALL
SELECT
MT.id,
MT.parent_id,
CAST(H.priority_string + '|' + REPLICATE('0', 10 - LEN(CAST(MT.[priority] AS VARCHAR))) + CAST(MT.[priority] AS VARCHAR) + '.' +
REPLICATE('0', 10 - LEN(CAST(MT.id AS VARCHAR))) + CAST(MT.id AS VARCHAR) AS VARCHAR(4000)) AS priority_string,
H.base,
H.lvl + 1
FROM
Hierarchy_CTE H
INNER JOIN My_Table MT ON MT.parent_id = H.id
)
SELECT
id,
base,
lvl
FROM
Hierarchy_CTE
ORDER BY
priority_string
I added padding zeros equal to a fixed length minus then "stringified" priority length and also for the id, so i can order them to the priority and then for id.
This solution works only in ascending orders (not work for descending orders with the maintenance of a tree view), but this list is useful for me only when i have to save updated priorities, so it may be enough.