One-2-many relation - need distinct counts

Hi gurus,

I have table A, B and need a distinct count of
Accounts from A. There is a one-2-many relation
between A and B. Accounts # in A are all unique.
However, in B there will be duplicates. So the
problem I have is, when I join as follows:
Select Count(Distinct(account_no))
from A, B
where A.Account_no = B.Account_no

I get the correct count. If I do this:
Select Count(Distinct(account_no)), B.Account_type
from A, B
where A.Account_no = B.Account_no
group by B.Account_type

I get wrong counts because there some are duplicated.
I tried everything that I can think of - subquery, sub
table etc. I would appreciate some help in writing
the query. Thanks in advance.

PS

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