joining a table to a user-defined function?

Suppose I have a SQL Server table named 'gadget'. 'gadget' has an integer field named 'gadget_key', which is the primary key of the table.

Now suppose I have a user-defined function named 'udf_gadget_values'. This function takes as its input parameter an integer variable named '@.nGadgetKey'. This function returns a table which will always contain exactly one record. This one record has one field named 'nGadgetKey', which contains the same value that was passed to the function in parameter '@.nGadgetKey'

I would like to join the table 'gadget' with the table that function 'udf_gadget_values' returns kind of like this:

SELECT TOP 10 *
FROM gadget, udf_gadget_values(gadget.gadget_key)

The purpose of this query is to get the top 10 records from 'gadget', as well as the values associated with each record, as returned by the function.

The real issue is this: how do I pass gadget.gadget_key to the function as an input parameter? Or if this will not work, is there an alternative?

Hi,

This syntax is neither supported in Yukon nor Shiloh. I believe the problem is that the output rowset cannot be materialized until the function is evaluated, and yet, the function cannot be evaluated until the output rowset is materialized.

In Yukon we've introduced a new relational operator called CROSS APPLY that you could use in scenarios like this. The LHS of CROSS APPLY is a table source and the RHS is a table-valued function. The formal input parameters of the function can be bound to actual column values materialized in the LHS rowset. In other words, for each row of the LHS, evaluate the function on the RHS and JOIN the results to the LHS, resulting in >=1 row in the ultimate output rowset. In essense, it solves the problem described above by assigning a formal and well-defined evaluation strategy to the LHS and RHS of the CROSS APPLY.

It would look like this:

select * from gadget cross apply udf_gadget_values(gadget_key)

Moreover, in Yukon, we've changed the parser to allow function input parameters to bind to correlated subqueries in FROM clause and in the projection list. The examples below illustrate:

-- Yukon : works
-- Shiloh: !works
select * from gadget where exists
(select * from udf_gadget_values(gadget.gadget_key))

-- Yukon : works
-- Shiloh: !works
select *
, (select gadget_desc
from dbo.udf_gadget_values(gadget.gadget_key))
as function_value
from gadget

Regards,
Clifford Dibble
Program Manager, SQL Server