We have an environment with several databases spread across multiple servers. Each database has the same DB schema.

Can I use Shards only to query those existing databases (i.e. never add data)? From reading the Shards docs, it seems to me that I'll have trouble because each DB will use the same keys/IDs to represent different data (e.g. customer ID 1 in the Customer table on System1 may reference a completely different customer on System2).

Thanks in advance.

Alternately, what happens if the same customer is in multiple DB's, but with a different key? I'm guessing that Shards won't be able to properly match the records to the same customer.

Hmm, no response?