Thread: SQL subquery (count distinct) - Any Ideas?

I'm trying to write a query to return the number of different customers 
called on a single day.  The database has a table called 'user', a table 
called 'caller_session' which references a 'user' record, and a table called 
'call' which references a 'caller_session'.  This is my current attempt:

select
user.name,
sum((select count(distinct call.customer_id) from call where 
call.caller_session_id=cs.caller_session_id)) as contacted
from user, caller_session cs
where cs.user_id=user.user_id
and date(cs.session_date) = date('2005-04-13')
group by user.name;

I get back a list of names and a call count (as desired), but the count is 
not correct!  The subqery is counting the number of different customers 
called for each caller_session, and summing them based on the user.name 
field.  If the same customer is called in 2 different sessions, this is 
being counted as 2 customers, but should be 1!

The 'contacted' count calculation has to be in a subquery as above, because 
there are other subqueries after this one to calculate other data based on 
the outer query (the outer query has to be as it is here).  Not quite sure 
where the sum, count and distinct should really go to get the required 
results!

Any help greatly appreciated!

On Wed, 2005-04-13 at 18:28 +0100, Matt Fulford wrote:
> I'm trying to write a query to return the number of different customers 
> called on a single day.  The database has a table called 'user', a table 
> called 'caller_session' which references a 'user' record, and a table called 
> 'call' which references a 'caller_session'.  This is my current attempt:

If I understand correct, this might work and still allow you to keep
your other subselects:
       SELECT tab.name,       sum(contacted) AS contacted,       ... subselects ...       FROM (SELECT user_id,
user.name,count(*) AS contacted               FROM user JOIN caller_session USING (user_id)               JOIN call
USING(caller_session_id)               WHERE date(cs.session_date) = date('2005-04-13')               GROUP BY user_id,
user.name)AS tab       JOIN caller_session USING (user_id)       GROUP BY user_id;
 

> select
> user.name,
> sum((select count(distinct call.customer_id) from call where 
> call.caller_session_id=cs.caller_session_id)) as contacted
> from user, caller_session cs
> where cs.user_id=user.user_id
> and date(cs.session_date) = date('2005-04-13')
> group by user.name;
> 
> I get back a list of names and a call count (as desired), but the count is 
> not correct!  The subqery is counting the number of different customers 
> called for each caller_session, and summing them based on the user.name 
> field.  If the same customer is called in 2 different sessions, this is 
> being counted as 2 customers, but should be 1!
> 
> The 'contacted' count calculation has to be in a subquery as above, because 
> there are other subqueries after this one to calculate other data based on 
> the outer query (the outer query has to be as it is here).  Not quite sure 
> where the sum, count and distinct should really go to get the required 
> results!
> 
> Any help greatly appreciated!
> 
> 
> 
> 
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> 
-- 

Hi
 I have modified the SQL query given by you and I hope the query given below will give you the correct count.  SELECT
U.USER_ID, U.NAME , COUNT(*) FROM USER U , CALL C , CALLER_SESSION CS  
WHERE C.CALLER_SESSION_ID = CS.CALLER_SESSION_ID AND U.USER_ID = CS.USER_ID AND CAST( CS.SESSION_DATE AS DATE ) = CAST(
'2005-04-13'AS DATE ) 
GROUP BY U.USER_ID

Regards,
R.Muralidharan

-----Original Message-----
From: Matt Fulford [mailto:mtfulford@yahoo.co.uk]
Sent: Wednesday, April 13, 2005 10:59 PM
To: pgsql-sql@postgresql.org
Subject: [SQL] SQL subquery (count distinct) - Any Ideas?


I'm trying to write a query to return the number of different customers
called on a single day.  The database has a table called 'user', a table
called 'caller_session' which references a 'user' record, and a table called
'call' which references a 'caller_session'.  This is my current attempt:

select
user.name,
sum((select count(distinct call.customer_id) from call where
call.caller_session_id=cs.caller_session_id)) as contacted
from user, caller_session cs
where cs.user_id=user.user_id
and date(cs.session_date) = date('2005-04-13')
group by user.name;

I get back a list of names and a call count (as desired), but the count is
not correct!  The subqery is counting the number of different customers
called for each caller_session, and summing them based on the user.name
field.  If the same customer is called in 2 different sessions, this is
being counted as 2 customers, but should be 1!

The 'contacted' count calculation has to be in a subquery as above, because
there are other subqueries after this one to calculate other data based on
the outer query (the outer query has to be as it is here).  Not quite sure
where the sum, count and distinct should really go to get the required
results!

Any help greatly appreciated!




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