SQL Server Function to Generate Random Numbers
By: Eli Leiba | Comments (1) | Related: More > TSQL
Problem
The request is to expand upon the SQL Server randomizing capabilities by creating a function that will generate a random number in many different ways, thus enabling the user to choose the randomizing generation approach from four different methods.
Solution
My solution involves creating a T-SQL function in the SQL Server master database, called GenRandomNumber.
This function gets a parameter called @method that defines the method of generating the random number.
The @method parameter can be one of these four possibilities:
| Method Value | Description |
|---|---|
| rand | Method uses the SQL built-in RAND() function to generate the random number |
| crypt | Method uses the SQL built-in CRYPT_GEN_RANDOM () function to generate the random number |
| newid | Method uses the SQL built-in NEWID() GUID built-in function generator to generate the random number |
| time | Method uses a combination of the DATEPART() and GETDATE() time function and RAND() function to generate the random number |
The function uses a CASE statement query that queries a pre-defined view that generates all possible random numbers as described in the table above. The resulting random number will be rounded to 6 digits precision.
The view is necessary because you cannot call a non-deterministic function inside of a user-defined function. If you try doing this, for example with the using the rand() function directly, you will encounter the following error message:
Msg 443, Level 16, State 1, Procedure GenRandomNumber, Line 24
Invalid use of a side-effecting operator 'rand' within a function.
In order to overcome this limitation, you create a view containing the call to the non-deterministic functions.
Here is the T-SQL code for the to create the view:
USE master GO CREATE VIEW VW_Random AS SELECT RAND () AS Val_Rand, NEWID () AS Val_NewId, ROUND (RAND ((DATEPART (mm, GETDATE ()) * 100000) + (DATEPART (ss, GETDATE ()) * 1000) + DATEPART (ms, GETDATE ())), 6) AS Val_Time, CRYPT_GEN_RANDOM (3) AS Val_crypt GO
SQL Server Function to Generate Random Numbers
USE master
GO
CREATE FUNCTION dbo.GenRandomNumber (@method VARCHAR (5))
RETURNS DECIMAL (8, 6)
-- ================================================================
-- Author: Eli Leiba
-- Create date: 07-2018
-- Function Name: dbo.GenRandomNumber
-- Description:
-- Generates a random number between 0 and 1 (3 digits)
-- supports four methods (@method is input parameter)
-- 1) 'rand' = using SQL built-in rand () function.
-- 2) 'newid' = using NEWID GUID generator.
-- 3) 'time' = using a time and rand built-in combination.
-- 4) 'crypt' = using the built-in CRYPT_GEN_RANDOM function.
-- ================================================================
AS
BEGIN
DECLARE @rand DECIMAL (8, 6)
SELECT @rand = CASE lower (@method)
WHEN 'rand'
THEN ROUND (Val_Rand, 6)
WHEN 'newid'
THEN 0.000001 * ABS (CAST (Val_NewId AS BINARY (6)) % 1000000)
WHEN 'time'
THEN Val_Time
WHEN 'crypt'
THEN 0.000001 * ABS (CAST (Val_crypt AS BINARY (6)) % 1000000)
ELSE ROUND (Val_Rand, 6)
END
FROM VW_Random
RETURN @rand
END
GO
Sample Execution
USE master
GO
SELECT dbo.GenRandomNumber ('newid') as method_by_newid_rand,
dbo.GenRandomNumber ('rand') as method_by_rand_rand,
dbo.GenRandomNumber ('crypt') as method_by_crypt_rand,
dbo.GenRandomNumber ('time') as method_by_time_rand
GO
And the results are as follows:
Next Steps
- You can create and compile this simple function as a UDF in your application or master database and use it as a simple TSQL tool for generating random numbers in all the four different methods.
- The stored procedure was tested with SQL Server 2014, but should work with all versions.
About the author
Eli Leiba is a senior application DBA, a teacher and a senior database consultant with 19 years of RDBMS experience.
View all my tips