Use RAND() in User Defined Function

Question

I am trying to create a user defined function which calls the system RAND() function inside it, when I try to create the function it errors out with the followi

Answer 1

One more idea: Use the function just to do the calculation for your business logic and hand in the non-deterministic part. In your case you seem to pick a random number between zero and the highest employeeID (what about missing IDs?)

As told before RAND() is difficult to use. It will come back with the same value in multiple calls. Therefore I use NEWID, cast it to VARBINARY(8) and cast this to BIGINT.

Have a look at this:

This function will take a GUID and scale it between the given borders:

CREATE FUNCTION dbo.GetRandomNumber(@lowerLimit BIGINT, @upperLimit BIGINT, @GuidValue UNIQUEIDENTIFIER)
RETURNS BIGINT
AS
BEGIN
    RETURN
    (
    SELECT ABS(CAST(CAST(@GuidValue AS VARBINARY(8)) AS BIGINT)) % (@upperLimit-@lowerLimit)+@lowerLimit
    )
END
GO

--This table will be filled with random values

CREATE TABLE testTable(RndNumber BIGINT,Tile INT);

--The CTE creates more than 6 mio dummy rows

WITH manyRows AS
(
    SELECT 1 AS nr FROM master..spt_values CROSS JOIN master..spt_values AS x
)
INSERT INTO testTable(RndNumber) 
SELECT dbo.GetRandomNumber(-300,700,NEWID()) --<-- Here I pass in the non-deterministic part
FROM manyRows;

--Now the table is tiled in 10 equal fragments

WITH UpdateableCTE AS
(
    SELECT Tile
          ,NTILE(10) OVER(ORDER BY RndNumber) AS tileValue
    FROM testTable
)  
UPDATE UpdateableCTE SET Tile=tileValue;

--check the random result

SELECT * FROM testTable
ORDER BY Tile,RndNumber;

--This shows clearly, that the covered range per tile is almost the same which is a proof for a fairly good random spread

SELECT Tile
      ,COUNT(*) CountOfNumbers
      ,MAX(RndNumber)-MIN(RndNumber) CoveredRange
FROM testTable
GROUP BY Tile
ORDER BY Tile;
GO

--clean up

DROP TABLE dbo.testTable;
DROP FUNCTION dbo.GetRandomNumber;

The result

T   Counts  min     max     CoveredRange
1   636553  -300    -201      99
2   636553  -201    -101     100
3   636553  -101       0     101
4   636553     0      99      99
5   636553    99     199     100
6   636553   199     299     100
7   636553   299     399     100
8   636553   399     499     100
9   636553   499     599     100
10  636552   599     699     100

You can see, that each tile covers roughly the same count of elements. The elements inside are covering almost the same range. This shows, that the numbers are evenly spread within the table.