Обсуждение: pesky select query

Hello ..

I'm having trouble figuring out a good way to return my desired results from
the following table ...

Table    = g_state_county_app
app_code                         | varchar() not null          
state_code                       | int4 not null                 
county_code                    | int4 not null                 
region_code                      | varchar()                 

The result I'm looking for, is that for each App_Code I would like the count
of distinct states.  

So, I may have a 1000 records, but only have 4 distinct app_codes and up to
50 distinct state_codes.  What I'd like to do is produce a query that will
list each app_code and the count of distinct states for that app_code on one
line.  I don't care what the state_code is, I just need to know the number
of distinct state_codes per app_code.

The data may look like this:

APP1, TX, 1, A1
APP1, TX, 2, A2
APP1, CO, 3, B4
APP2, IL, 1, A3

And the result I want is this:

APP1,    2        # App1 is found in 2 distinct states
APP2,    1        # App2 is found in 1 distinct states

So far I've tried variations of select distincts with counts() and group
by's on various fields.   I briefly considered trying to do this with an
outer join, but I'm not sure it'd work. I'm still using 6.5.x so I'd have to
simulate it with a union all/subquery.  For that reason I thought'd I'd ask
here first to see if there is a better way.

Thanks,
Bryan

"Ingram, Bryan" <BIngram@sixtyfootspider.com> writes:
> What I'd like to do is produce a query that will
> list each app_code and the count of distinct states for that app_code on one
> line.  I don't care what the state_code is, I just need to know the number
> of distinct state_codes per app_code.

> So far I've tried variations of select distincts with counts() and group
> by's on various fields.   I briefly considered trying to do this with an
> outer join, but I'm not sure it'd work. I'm still using 6.5.x so I'd have to
> simulate it with a union all/subquery.  For that reason I thought'd I'd ask
> here first to see if there is a better way.

Update to 7.0.* and do select app_code, count(distinct state_code) from tab group by app_code;
        regards, tom lane