OK, all done. I had to include the RAND in the wrapper view too, for the same reason.

Here is the full script:

USE tempdb;

-- Drop the in-line function

IF OBJECT_ID(N'dbo.GetSourceSample', N'IF')

IS NOT NULL

DROP FUNCTION dbo.GetSourceSample

GO

-- Drop the view wrapping NEWID

IF OBJECT_ID(N'dbo.Random', N'V')

IS NOT NULL

DROP VIEW dbo.Random;

GO

-- Drop the combinations table

IF OBJECT_ID(N'dbo.Combinations', N'U')

IS NOT NULL

DROP TABLE dbo.Combinations;

GO

-- Drop our test table

IF OBJECT_ID(N'dbo.Source', N'U')

IS NOT NULL

DROP TABLE dbo.Source;

GO

-- Create numbers table if required

IF OBJECT_ID(N'dbo.Number', N'U')

IS NULL

BEGIN

CREATE TABLE dbo.Number (n SMALLINT PRIMARY KEY);

-- 736 SMALLINTs exactly fill one 8K page

INSERT dbo.Number (n)

SELECT TOP (736)

ROW_NUMBER() OVER (ORDER BY (SELECT 0))

FROM master.sys.columns C1,

master.sys.columns C2,

master.sys.columns C3;

END;

GO

-- Create the test table

CREATE TABLE dbo.Source

(

row_id INTEGER IDENTITY PRIMARY KEY,

vehicle_type CHAR(1) NOT NULL,

vehicle_id INTEGER NOT NULL

);

GO

-- View wrapping NEWID

CREATE VIEW dbo.Random

WITH SCHEMABINDING

AS SELECT n = RAND(CHECKSUM(NEWID()));

GO

-- All possible combinations of values [3...19]

-- that sum to 25

SELECT row_id = IDENTITY(INT, 0, 1),

nc = C.n,

nt = T.n,

nr = R.n

INTO dbo.Combinations

FROM dbo.Number C,

dbo.Number T,

dbo.Number R

WHERE C.n BETWEEN 3 AND 19

AND T.n BETWEEN 3 AND 19

AND R.n BETWEEN 3 AND 19

AND C.n + T.n + R.n = 25

-- Create clustered primary key

ALTER TABLE dbo.Combinations

ADD PRIMARY KEY (row_id)

WITH (FILLFACTOR = 100);

GO

-- Add 100,000 random rows, roughly evenly distributed

-- across vehicle types

INSERT dbo.Source

(

vehicle_type,

vehicle_id

)

SELECT TOP (100000)

CASE

-- Chance of being a car

WHEN RAND(CHECKSUM(NEWID(), N1.n)) <= 0.3333 THEN 'C'

-- Chance of being a truck

WHEN RAND(CHECKSUM(NEWID(), N2.n)) <= 0.3333 THEN 'T'

-- Chance of being an RV

ELSE 'R'

END,

-- Random vehicle id

ABS(CHECKSUM(NEWID()))

FROM dbo.Number N1,

dbo.Number N2,

dbo.Number N3;

GO

-- A helpful index

CREATE UNIQUE INDEX [UQ dbo.Source vehicle_type, row_id (vehicle_id)]

ON dbo.Source

(vehicle_type ASC, row_id ASC)

INCLUDE (vehicle_id)

WITH (FILLFACTOR = 100);

GO

-- Show the number of vehicles of each type

SELECT vehicle_type,

row_count = COUNT_BIG(*)

FROM dbo.Source

GROUP BY

vehicle_type

ORDER BY

vehicle_type;

GO

-- Create the function

CREATE FUNCTION dbo.GetSourceSample ()

RETURNS TABLE

WITH SCHEMABINDING

AS RETURN

WITH SelectionCounts

AS (

-- Number of rows to select from each group

-- Minimum 3, total for all groups = 25

-- Choose one of the possible combinations at random

SELECT TOP (1)

nc = C.n,

nt = T.n,

nr = R.n

FROM dbo.Number C,

dbo.Number T,

dbo.Number R

WHERE C.n BETWEEN 3 AND 19

AND T.n BETWEEN 3 AND 19

AND R.n BETWEEN 3 AND 19

AND C.n + T.n + R.n = 25

ORDER BY

(SELECT R.n FROM dbo.Random R)

),

GroupCounts

AS (

--Find the total number of vehicles of each type

SELECT vehicle_type,

group_size = COUNT_BIG(*)

FROM dbo.Source

WHERE vehicle_type = 'C'

GROUP BY

vehicle_type

UNION ALL

SELECT vehicle_type,

group_size = COUNT_BIG(*)

FROM dbo.Source

WHERE vehicle_type = 'T'

GROUP BY

vehicle_type

UNION ALL

SELECT vehicle_type,

group_size = COUNT_BIG(*)

FROM dbo.Source

WHERE vehicle_type = 'R'

GROUP BY

vehicle_type

),

Parameters

AS (

SELECT GC.group_size,

GC.vehicle_type,

sample_size =

CASE GC.vehicle_type

WHEN 'C' THEN SC.nc

WHEN 'T' THEN SC.nt

WHEN 'R' THEN SC.nr

ELSE 0

END

FROM GroupCounts GC,

SelectionCounts SC

),

RandomRows

AS (

-- Generate a random row number for each row required from

-- each group. Maximum rows returned = 25 * group_count

--

-- The TOP (9223372036854775807 (= BIGINT.Max)) is just to

-- force the query plan to calculate the random row number

-- before the final join

SELECT TOP (9223372036854775807)

P.vehicle_type,

Random.rn

FROM Parameters P

CROSS

APPLY (

SELECT TOP (P.sample_size)

rn = CONVERT(BIGINT, R.n * P.group_size + 1)

FROM dbo.Number N,

dbo.Random R

ORDER BY

N.n ASC

) Random

ORDER BY

P.vehicle_type,

Random.rn

),

NumberedSourceRows

AS (

-- Number the source rows, restarting the numbering for each group

SELECT S.row_id,

S.vehicle_type,

S.vehicle_id,

rn = ROW_NUMBER() OVER (PARTITION BY S.vehicle_type ORDER BY S.row_id ASC)

FROM dbo.Source S

)

-- Fetch the numbered rows that match the random row number, per group

SELECT NSR.row_id,

NSR.vehicle_type,

NSR.vehicle_id

FROM RandomRows RR

JOIN NumberedSourceRows NSR

ON NSR.vehicle_type = RR.vehicle_type

AND NSR.rn = RR.rn;

GO

SET STATISTICS TIME ON;

SELECT GSS.row_id,

GSS.vehicle_type,

GSS.vehicle_id

FROM dbo.GetSourceSample() GSS;

SET STATISTICS TIME OFF;

GO

-- Drop the in-line function

IF OBJECT_ID(N'dbo.GetSourceSample', N'IF')

IS NOT NULL

DROP FUNCTION dbo.GetSourceSample

-- Drop the view wrapping NEWID

IF OBJECT_ID(N'dbo.Random', N'V')

IS NOT NULL

DROP VIEW dbo.Random;

-- Drop the combinations table

IF OBJECT_ID(N'dbo.Combinations', N'U')

IS NOT NULL

DROP TABLE dbo.Combinations;

-- Drop our test table

IF OBJECT_ID(N'dbo.Source', N'U')

IS NOT NULL

DROP TABLE dbo.Source;

Plan stayed exactly the same, 94ms average CPU time.