SQL to move rows up or down in two-table arrangement - sql

Question

I have two tables that I designed this way with a possible reshuffling of elements in mind:
1. [dbo.test_db_002] with columns:
[id] = INT NOT NULL IDENTITY(1,1) PRIMARY KEY
[name] = NVARCHAR(255)
and
2. [dbo.test_db_003] with columns:
[ord] = INT
[itmid] = INT NOT NULL PRIMARY KEY
[itmid] column has a constraint linking it to [dbo.test_db_002].[id] like so:
ALTER TABLE [dbo.test_db_003]
ADD CONSTRAINT fk1 FOREIGN KEY ([itmid])
REFERENCES [dbo.test_db_002]([id])
ON DELETE CASCADE ON UPDATE CASCADE;
Say, [dbo.test_db_002] table has the following data:
[id] [name]
3 John
5 Mary
8 Michael
10 Steve
13 Jack
20 Pete
and [dbo.test_db_003] has the following ordering data:
[ord] [itmid]
1 5
4 8
5 13
8 3
10 10
13 20
So when I retrieve names from the database I use the following SQL:
SELECT [name]
FROM [dbo.test_db_002] t1
LEFT JOIN [dbo.test_db_003] t2 ON t1.[id]=t2.[itmid]
ORDER BY t2.[ord] ASC
It produces the list of names (ordered by the [dbo.test_db_003].[ord] column):
Mary
Michael
Jack
John
Steve
Pete
What I am looking for is an option to move each of the names up and down the list. For instance, if I want to move "John" one position up, what do I do?
So far I came up with this partial SQL:
WITH cte AS
(
SELECT [id], [ord], ROW_NUMBER() OVER (ORDER BY t2.[ord] ASC) AS rowNum
FROM [dbo.test_db_002] t1
LEFT JOIN [dbo.test_db_003] t2 ON t1.[id] = t2.[itmid]
)
That will select the following:
rowNum [id] [ord]
1 1 5
2 4 8
3 5 13
4 8 3
5 10 10
6 13 20
So I understand that I need to shift values in [ord] column up by one starting from the index 3 (since "John" index is 4) and then somehow make "John"'s [ord] to be set to 5, but how do you do that?

Answer 1

I prepared a complete demo for you how this can work on data.stackexchange.com.
The solution is tailored to your comment:
the move up or down can be only a single step - in other words, one
cannot move 2 or more positions
In the example I make John trade ordinal positions with Jack above him:
WITH x AS (
SELECT t2.itmid, t2.ord
FROM dbo.test_db_002 t1
LEFT JOIN dbo.test_db_003 t2 ON (t1.id = t2.itmid)
WHERE t1.name = 'John' -- must be unique, or query by id ...
)
, y AS (
SELECT TOP 1
t.itmid, t.ord
FROM dbo.test_db_003 t, x
WHERE t.ord < x.ord -- smaller ord = "above"
ORDER BY t.ord DESC
)
UPDATE dbo.test_db_003 SET ord = z.ord
FROM (
SELECT x.itmid, y.ord FROM x,y
UNION ALL
SELECT y.itmid, x.ord FROM x,y
) z
WHERE dbo.test_db_003.itmid = z.itmid
###Major points:
Use two CTE to structure the query:
Get John's id & ordinal position
Get the same for the person above him
Prepare two rows where these two switch ordinal numbers with the help of UNION ALL
Use these two rows in a now simple UPDATE
The ordinal position ord must allow passing duplicates for this to work.
If there is nobody 'above', the query will silently do nothing.