Question

I have 2 tables: Items & Users.

Items contains ItemID, and Num_Users
Users contains UserID

For each ItemID, I need to randomly select a number of Users according to the value stated in the Num_Users column.

I created a sample set of data on SQL Fiddle.

Answer 1

One way. SQL Fiddle

SELECT Items.[ItemID],
       UserID
FROM   Items
       OUTER APPLY (SELECT TOP ([Num_Users]) *
                    FROM   Users
                    ORDER  BY Newid()) A 

You could also use CRYPT_GEN_RANDOM(4) instead of Newid() for a greater degree of randomness but there are some issues with this on non up-to-date versions of SQL Server 2008.