Question

I have a UDF that takes a table as a parameter (a 2 column table) and outputs a string, much like this article. I have a table that I want to apply the UDF over multiple columns like this:

Date   Unit   Line   Revenue   Orders
4/1/12 D      R      20.00     3
4/2/12 D      R      25.00     4
4/1/12 H      W      33.00     1
4/2/12 H      W      35.00     3

I want to call my UDF on every row of this table that has the most current date and pass the UDF a table with the columns Date and Revenue for each distinct Unit and Line. And I also want to call the UDF and pass Date and Orders for each distinct Unit and Line. This is a report and the UDF will always get passed the Date column and another column that I want to apply some calculation to and store and report. So I have looked at a lot of things including CROSS APPLY and I want to do something like this:

SELECT        T.unit
              , T.line
              , dbo.fn_myUDF((SELECT T2.Date, T2.Revenue FROM #Table T2)) as UDFRevenueResult
              , dbo.fn_myUDF((SELECT T2.Date, T2.Orders FROM #Table T2)) as UDFOrderResult
FROM          #Table T
WHERE         T.Date = @ReportDate

This gives me the error “Only one expression can be specified in the select list when the subquery is not introduced with EXISTS.” I looked at CROSS APPLY but that seems only apply for when you are returning a table variable. So I could probably answer my own question by using a cursor and a loop maybe and constructing each table I want to pass to the UDF in each loop iteration but that just doesn’t seem right. Can anyone give me an idea how to do what I want in SQL Server 2008?

Answer 1

Subqueries can’t be used like that to return table variables in the SELECT portion of the query. They can only return a single value. As in:

set @myParam = (select myvalue from table where primarykey = 1)

or

set @myParam = (select top 1 myvalue from table)

But, considering that your subqueries do not have any relation to the rows being selected, you can do something like this.

declare @t1 table (DateTime c1, float c2)
insert @t1
SELECT Date, Revenue 
FROM #Table 

declare @t2 table (DateTime c1, int c2) -- not sure on data type of 'Orders'
insert @t2
SELECT Date, Orders FROM #Table


SELECT T.unit               
     , T.line               
     , dbo.fn_myUDF(@t1) as UDFRevenueResult               
     , dbo.fn_myUDF(@t2) as UDFOrderResult 
FROM #Table T 
WHERE T.Date = @ReportDate