Rownum order is incorrect after join - SQL Server - sql

Question

http://sqlfiddle.com/#!18/97fbe/1 - fiddle
I have tried to demo my real life scenario as much as possible
Tables:
CREATE TABLE [OrderTable]
(
[id] int,
[OrderGroupID] int,
[Total] int,
[fkPerson] int,
[fkitem] int
PRIMARY KEY (id)
)
INSERT INTO [OrderTable] (id, OrderGroupID, Total ,[fkPerson], [fkItem])
VALUES
('1', '1', '20', '1', '1'),
('2', '1', '45', '2', '2'),
('3', '2', '32', '1', '1'),
('4', '2', '30', '2', '2'),
('5', '2', '32', '1', '1'),
('6', '2', '32', '3', '1'),
('7', '2', '32', '4', '1'),
('8', '2', '32', '4', '1'),
('9', '2', '32', '5', '1');
CREATE TABLE [Person]
(
[id] int,
[Name] varchar(32)
PRIMARY KEY (id)
)
INSERT INTO [Person] (id, Name)
VALUES
('1', 'Fred'),
('2', 'Sam'),
('3', 'Ryan'),
('4', 'Tim'),
('5', 'Gary');
CREATE TABLE [Item]
(
[id] int,
[ItemNo] varchar(32),
[Price] int
PRIMARY KEY (id)
)
INSERT INTO [Item] (id, ItemNo, Price)
VALUES
('1', '453', '23'),
('2', '657', '34');
Query:
WITH TABLE1 AS
(
SELECT
-- P.ID AS [PersonID],
-- P.Name,
SUM(OT.[Total]) AS [Total],
i.[id] AS [ItemID],
ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS rownum,
ot.fkperson,
[fkItem]
FROM
OrderTable OT
-- INNER JOIN Person P ON P.ID = OT.fkperson
INNER JOIN
Item I ON I.[id] = OT.[fkItem]
GROUP BY
-- P.ID, P.Name,
i.id, ot.fkperson, [fkItem]
)
SELECT
t1.[fkperson],
P.[Name],
t1.[itemid],
t1.[total],
t1.[rownum]
-- Totalrows = (SELECT MAX(rownum) FROM TABLE1)
FROM
TABLE1 T1
INNER JOIN
Person P ON P.ID = T1.fkperson
INNER JOIN
Item I ON I.[id] = T1.[fkItem]
Result:
| fkperson | Name | itemid | total | rownum |
+----------+------+--------+-------+--------+
| 1 | Fred | 1 | 84 | 1 |
| 3 | Ryan | 1 | 32 | 2 |
| 4 | Tim | 1 | 64 | 3 |
| 5 | Gary | 1 | 32 | 4 |
| 2 | Sam | 2 | 75 | 5 |
which is the result I want. However, my real-life example is giving me the row number in a weird order. I know its an issue with a join because when i comment these join:
INNER JOIN
Person P ON P.ID = T1.fkperson
INNER JOIN
Item I ON I.[id] = T1.[fkItem]
out it works fine.
| fkperson | Name | itemid | total | rownum |
|----------|------|--------|-------|--------|
| 1 | Fred | 1 | 84 | 4 |
| 3 | Ryan | 1 | 32 | 3 |
| 4 | Tim | 1 | 64 | 5 |
| 5 | Gary | 1 | 32 | 1 |
| 2 | Sam | 2 | 75 | 2 |
Has anyone got any advice on how the join would be causing these weird rownumber ordering? Or point me in the right direction. Thanks

Answer 1

Any relational database is inherently UNordered - and you won't get any guaranteed order UNLESS you explicitly ask for it - by means of an ORDER BY clause on your outer query.
You need to add the ORDER BY explicitly - like this:
WITH TABLE1 AS
(
.....
)
SELECT
(list of columns ....)
FROM
TABLE1 T1
INNER JOIN
Person P ON P.ID = T1.fkperson
INNER JOIN
Item I ON I.[id] = T1.[fkItem]
ORDER BY
T1.rownum

Answer 2

You are using order by (select null). That means indeterminate ordering. And the order can change from one invocation of the query to another.
You should not be depending on default ordering, even by an external order by. If you want values in a particular order, specify that ordering explicitly in the order by in the windowing clause.