Using Criteria to Count Unique Values

[bryan0]

Hello, I've searched for a couple of hours and am stuck. I have 3 tables, and need to count the unique values in one of them...

Table: SUPPLIER

SUPPLIER_ID	SUPPLIER_NAME
S-91	IBM
S-92	Dell
S-93	Lenovo
S-94	Lenovo

Table: POS

SUPPLIER_ID	SITE	PO_NUMBER	ORDER_VALUE
S-91	Location A	451	$5
S-92	Location B	452	$10
S-93	Location C	453	$12
S-93	Location B	454	$7
S-93	Location D	455	$18
S-92	Location D	456	$20
S-93	Location C	457	$6
S-94	Location C	458	$9

Table: SITE

SITE_DESCRIPTION	COUNTRY
Location A	USA
Location B	Switzerland
Location C	Switzerland
Location D	Brazil

I want to be able to use the SUPPLIER as a criteria, and count the number of unique Buying Locations being used for each country. For example, if I was looking at Lenovo, I'd want to see that Switerland is buying Lenovo products from 2 sites (Locations B and C) and Brazil is buying from 1 site (Location D):
Switzerland - 2
Brazil - 1

I've gotten it to work using a nested SELECT statement, but it's counting all of the times the supplier name is listed in the PURCHASE_ORDERS table (it's giving me 4 for Switzerland, not 2.) Here's what I'm using:

SELECT DISTINCT SUPPLIER.SUPPLIER_NAME, SITE.COUNTRY, Count(*) AS Number_of_Sites
FROM (POS LEFT JOIN (SITE LEFT JOIN (SELECT DISTINCT SITE_DESCRIPTION FROM SITE)  
AS T ON SITE.SITE_DESCRIPTION = T.SITE_DESCRIPTION) 
ON POS.SITE_ID = SITE.SITE_ID) 
RIGHT JOIN SUPPLIER ON POS.SUPPLIER_ID = SUPPLIER.SUPPLIER_ID
GROUP BY SUPPLIER.SUPPLIER_NAME, SITE.COUNTRY
HAVING (((SUPPLIER.SUPPLIER_NAME)="Lenovo"));

Any help would be greatly appreciated!

[June7]

There is no SITE_ID fields shown in POS or SITE tables. Is this autonumber primary key in SITE and foreign key in POS?

SELECT Q.Supplier_Name, Q.Country, Count(Q.Site_Description) AS Number_of_Sites
FROM (SELECT DISTINCT Site.Site_Description, Supplier.Supplier_Name, Site.Country
FROM (POS INNER JOIN Site ON POS.Site_ID = Site.Site_ID) INNER JOIN Supplier ON POS.Supplier_ID = Supplier.Supplier_ID) AS Q
GROUP BY Q.Supplier_Name, Q.Country;