Tip

Get a random sample of rows in SQL Server 2000

There are occasions when a random sample of a query's rows are needed. A simple but non-functioning solution is to include the system random number generator function within the query. Unfortunately, a single random number is generated for the query when what is desired is a random number for each row.

Another solution that is only available with SQL Server 2000 is to use a User Defined Function (UDF) to wrap the system random number generator. Since UDFs are invoked on a row-by-row basis, this approach theoretically could work. Unfortunately (again), Microsoft has restricted the usage of nondeterministic system functions that change the global state of the database. This includes the usage of the random number generator.

But there is a workaround for non-deterministic functions, which is to first create a view, then create a UDF that selects from the view and finally, reference the UDF in the query. Here's an example:

use master
go
create view dbo.RandomNumbers
(RandomNumber)
as select rand( ) as RandomNumber
GO
CREATE FUNCTION dbo.RandomNumberGet ( )
RETURNS real
AS
BEGIN
declare @r real
set @r = (select RandomNumber from RandomNumbers)
return @r
END
go
use Northwind
go
select  RandomNumber 
, OrderID
,  CustomerID
,  EmployeeID
FROM  (select  CAST(master.dbo.RandomNumberGet() * 100 as integer)  as RandomNumber
, OrderID
,  CustomerID
,  EmployeeID
from  Orders
) As RandomOrders
Order by RandomNumber


    Requires Free Membership to View

This was first published in February 2005

There are Comments. Add yours.

 
TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to:

Disclaimer: Our Tips Exchange is a forum for you to share technical advice and expertise with your peers and to learn from other enterprise IT professionals. TechTarget provides the infrastructure to facilitate this sharing of information. However, we cannot guarantee the accuracy or validity of the material submitted. You agree that your use of the Ask The Expert services and your reliance on any questions, answers, information or other materials received through this Web site is at your own risk.