Обсуждение: 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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On Tuesday 26 August 2003 14:54, PS PS wrote:
> 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.

I'm not sure the query is well formed. If you have the following in B:

Acct_type | Acct_no
alpha     | 0001
beta      | 0002
alpha     | 0003
beta      | 0003

I think you're saying you get:

alpha  2
beta   2

Are you saying you want

alpha  2
beta   1

or:

alpha  1
beta   2

If you're not sure which you want, that's the route of your problem. If you 
want the first try something like

SELECT account_no, min(account_type) FROM B GROUP BY account_no

--  Richard Huxton Archonet Ltd