In SQLSERVER 2005, I'm using table-valued function as a convenient way to perform arbitrary aggregation on subset data from large table (passing date range or such parameters).

I'm using theses inside larger queries as joined computations and I'm wondering if the query plan optimizer work well with them in every condition or if I'm better to unnest such computation in my larger queries.

1. Does query plan optimizer unnest table-valued functions if it make sense?
2. If it doesn't, what do you recommend to avoid code duplication that would occur by manually unnesting them?
3. If it does, how do you identify that from the execution plan?

code sample:

create table dbo.customers (
	[key] uniqueidentifier
	, constraint pk_dbo_customers
		primary key ([key])
)
go

/* assume large amount of data */
create table dbo.point_of_sales (
	[key] uniqueidentifier
	, customer_key uniqueidentifier
	, constraint pk_dbo_point_of_sales
		primary key ([key])
)
go

create table dbo.product_ranges (
	[key] uniqueidentifier
	, constraint pk_dbo_product_ranges
		primary key ([key])
)
go

create table dbo.products (
	[key] uniqueidentifier
	, product_range_key uniqueidentifier
	, release_date datetime
	, constraint pk_dbo_products 
		primary key ([key])
	, constraint fk_dbo_products_product_range_key 
		foreign key (product_range_key) 
		references dbo.product_ranges ([key])
)
go

.

/* assume large amount of data */
create table dbo.sales_history (
	[key] uniqueidentifier
	, product_key uniqueidentifier
	, point_of_sale_key uniqueidentifier
	, accounting_date datetime
	, amount money
	, quantity int
	, constraint pk_dbo_sales_history
		primary key ([key])
	, constraint fk_dbo_sales_history_product_key
		foreign key (product_key)
		references dbo.products ([key])
	, constraint fk_dbo_sales_history_point_of_sale_key
		foreign key (point_of_sale_key)
		references dbo.point_of_sales ([key])
)
go

create function dbo.f_sales_history_..snip.._date_range
(
    @accountingdatelowerbound datetime,
         @accountingdateupperbound datetime
)
returns table as
return (
	select
                  pos.customer_key
	    , sh.product_key
	    , sum(sh.amount) amount
	    , sum(sh.quantity) quantity
	from 
	    dbo.point_of_sales pos
	    inner join dbo.sales_history sh 
	        on sh.point_of_sale_key = pos.[key]
	where
                  sh.accounting_date between 
                      @accountingdatelowerbound and 
                      @accountingdateupperbound
	group by
                  pos.customer_key
                  , sh.product_key
)
go

-- TODO: insert some data

-- this is a table containing a selection of product ranges
declare @selectedproductranges table([key] uniqueidentifier)

-- this is a table containing a selection of customers
declare @selectedcustomers table([key] uniqueidentifier)

declare @low datetime
	, @up datetime

-- TODO: set top query parameters

.

select
         saleshistory.customer_key
         , saleshistory.product_key
         , saleshistory.amount
         , saleshistory.quantity
from
         dbo.products p
         inner join @selectedproductranges productrangeselection 
             on p.product_range_key = productrangeselection.[key]
         inner join @selectedcustomers customerselection on 1 = 1
         inner join 
         dbo.f_sales_history_..snip.._date_range(@low, @up) saleshistory
             on saleshistory.product_key = p.[key]
             and saleshistory.customer_key = customerselection.[key]

I hope the sample makes sense.

Much thanks for your help!