TSQL USE ROW_NUMBER IN CTE, SELECT ORDER BY NOT WORKING

Question

I preapare string from row of nubmers. When I use the row_number function, the order by clause not working

DECLARE @text VARCHAR(MAX)

IF OBJECT_ID('tempdb..#numbers') IS NOT NULL DROP TABLE #numbers
SELECT CAST(ROW_NUMBER() OVER (ORDER BY name) AS INT) AS number INTO #numbers FROM master..spt_values 

SET     @text = ''

;WITH 
numbers (number)
AS
(
    SELECT CAST(ROW_NUMBER() OVER (ORDER BY name) AS INT) AS number FROM master..spt_values 
),
a
AS
(
    SELECT number FROM numbers WHERE number < 10
),
b
AS
(
    SELECT number FROM numbers WHERE number < 10
)
SELECT      @text = @text + LTRIM(STR(a.number*b.number))
FROM        a
CROSS JOIN  b
ORDER BY    a.number, b.number DESC

SELECT @text

result "9"

SET     @text = ''

;WITH 
numbers (number)
AS
(
    SELECT number FROM #numbers
),
a
AS
(
    SELECT number FROM numbers WHERE number < 10
),
b
AS
(
    SELECT number FROM numbers WHERE number < 10
)
SELECT      @text = @text + LTRIM(STR(a.number*b.number))
FROM        a
CROSS JOIN  b
ORDER BY    a.number, b.number DESC

SELECT @text

result "9876543211816141210864227242118151296336322824201612844540353025201510554484236302418126635649423528211477264564840322416881726354453627189"

Where is diference ?

Not a bug. Don't report it on connect. It will be closed as all these were http://stackoverflow.com/a/15163136/73226. Use a documented approach such as `XML` — Martin Smith, Aug 28 '15 at 10:15
@MartinSmith Yep, realised that, was just about to delete that comment when I realised it was to do with variable concatenation. In fact, I will delete it anyway as it is nonsense. — GarethD, Aug 28 '15 at 10:21

GarethD · Answer 1 · 2015-08-28T10:32:07.377

I expect this is related to this issue, in summary when you use variable concatenation, e.g.

SELECT @Variable = @Variable + someField
FROM    Table
ORDER BY AnotherField;

The results are dependant on physical implementation and internal access paths. I am currently struggling to find benchmark tests on the internet, but I think the fastest, reliable approach in SQL Server is to use XML extensions to concatenate rows to columns:

WITH Numbers AS (SELECT * FROM (VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9)) t (Number))
SELECT [Text] = (SELECT LTRIM(STR(a.number*b.number))
                FROM    Numbers AS A 
                        CROSS JOIN Numbers AS B
                ORDER BY A.Number, b.Number DESC
                FOR XML PATH(''), TYPE).value('.', 'VARCHAR(MAX)');

N.B. I have also removed the reference to master..spt_values and replaced with a table value constructor - this just adds unnecessary reads to generate a sequence from 1 to 9.

If you need more numbers for your sequence I would still not use system tables, use Iztik Ben-Gan's stacked CTE approach, as described in this article:

DECLARE @Numbers INT = 100000;

WITH N1 AS (SELECT N FROM (VALUES (1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) t (N)),
N2 (N) AS (SELECT 1 FROM N1 AS N1 CROSS JOIN N1 AS N2),
N3 (N) AS (SELECT 1 FROM N2 AS N1 CROSS JOIN N2 AS N2),
N4 (N) AS (SELECT 1 FROM N3 AS N1 CROSS JOIN N3 AS N2),
Numbers (Number) AS (SELECT TOP (@Numbers) ROW_NUMBER() OVER(ORDER BY N) FROM N4)

SELECT  Number
FROM    Numbers;

Lukasz Szozda · Answer 2 · 2015-08-28T09:40:20.650

Do not use cast on ROW_NUMBER(). This will return same as your second query:

DECLARE @text VARCHAR(MAX) = ''

;WITH 
numbers (number)
AS
(
    SELECT ROW_NUMBER() OVER (ORDER BY name)  AS number FROM master..spt_values 
),
a
AS
(
    SELECT number FROM numbers WHERE number < 10
),
b
AS
(
    SELECT number FROM numbers WHERE number < 10
)
SELECT      @text = @text + LTRIM(STR(a.number*b.number))
FROM        a
CROSS JOIN  b
ORDER BY    a.number, b.number DESC

Also don't define twice the same in CTE use aliases instead:

DECLARE @text VARCHAR(MAX) = ''

;WITH 
numbers (number)
AS
(
    SELECT ROW_NUMBER() OVER (ORDER BY name) AS number FROM master..spt_values 
),
a
AS
(
    SELECT number FROM numbers WHERE number < 10
)
SELECT      @text = @text + LTRIM(STR(a.number*b.number))
FROM        a AS a
CROSS JOIN  a AS b
ORDER BY    a.number, b.number DESC

SELECT @text

TSQL USE ROW_NUMBER IN CTE, SELECT ORDER BY NOT WORKING

2 Answers2

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