SELECT
    *
FROM
    tbl_order o
INNER JOIN
    tbl_contact c
ON
    c.ContactId = o.BillingContactId

The above query for an e-commerce store is nice and simple.

If I were to move all of my contacts data into a CRM such that its stored in a different database and the e-commerce database references contacts via a guid and fetches their data via a WCF service, how would I create an equivalent query?

Would this be too slow and ought I instead keep a copy of the contacts data in the e-commerce database?

I vote against copying the contacts data. Was it proved to be slow calling the WCF service?

I haven't tried it yet. How would the equivalent query be written?

Ian wrote:

I haven't tried it yet. How would the equivalent query be written?

I don't understand that question. I mean: if you have two tables on different DBs and you access the 'contact' table with a service, then I only can think on running your SELECT 'tbl_order', then with those contact_id you should look for them in the other service and do a lookup text/combo in your GUI. Am I missing something?

I guess not. I wasn't sure whether there was a fancier way of doing it.