Multiple Unions Where There Are No Results In First Set Causes All Following Unions To Return Nothing.

I have two tables one with current data and a second with the same design that holds purged history.

I was going to create view and then jsut use a where clause to filter both tables but I figured it would be faster if the where clause was passed into each query as opposed to the whoel view having to load and then be filtered.

Select PatientName, MemberId
FROM CLAIMS
WHERE MemberID = @MemberID
UNION
Select PatientName, MemberId
FROM CLAIMSHistory
WHERE MemberID = @MemberID

But it appears that if there are no records in the first statement that the whole thing fails. I tried the union all operator with out any luck either.

Now if had a view like this;
Create view vAllClaims as
Select PatientName, MemberId
FROM CLAIMS
UNION
Select PatientName, MemberId
FROM CLAIMSHistory


And said select * from vAllClaims where memberid = 12345 would the query optimizer put the build the where statement onto each subquery or pull all the data first and query it?