Message-ID: <6304397.post@talk.nabble.com>
Date: Thu, 14 Sep 2006 05:02:25 -0700 (PDT)
From: zqzuk <ziqi.zhang@hotmail.com>
To: pgsql-sql@postgresql.org
Subject: nested select within a DISTINCT block
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Hi, here i have a problem with this task...

I have a table "cancellation" which stores cancelled bookings and details of
charges etc
and a table "bookings" which stores details of bookings, for example:

cancellation(cancellation_id, booking_id, charge)
booking(booking_id, customer_id, product_package_id, details)

in the query, i wish to find, how many customers have booked for each
product_package_id. if there were 3 bookings for product_package_id=1, and
all these are cancelled and therefore exist in cancellation, then the query
result shoud display something like

package_id,   #of bookings
1                  0


here are what i tried

select distinct b.product_package_id, 
count (distinct b.customer_id and not exists (select cc from cancellation cc
where cc.booking_id=b.booking_id)) from booking as b
group by b.product_package_id

and it doesnt work. the syntax within the DISTINCT is wrong, unsurprisingly.


i also tried
select distinct b.product_package_id, 
count (distinct b.customer_id not in (select cc from cancellation cc where
cc.booking_id=b.booking_id)) from booking as b
group by b.product_package_id

it produced incorrect result. ie, for those canceled bookings are also
counted, producing
package_id,   #of bookings
1                  3

which supposed to be
package_id,   #of bookings
1                  0


could anyone give any hints please, many thanks !
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