Re: Need magical advice for counting NOTHING

In response to Andreas :
> Hi,
> The source select counts log-events per user.
> All is well when a user has at least one event per log_type in the log
> within a given timespan.
> If one log_type is missing COUNT() has nothing to count and there is
> expectedly no result line that says 0.
> BUT I need this 0-line because of a crosstab. :(
> I need to know how to prevent in my crosstab categories on the right to
> slip to the left, when the left category is emptyy.
>
> Server 8.3.5
>
> 3 tables
> log (log_id, log_type_fk, user_fk, ts timestamp, ...)
> users (user_id, user_name, ...)
> log_type (log_type_id, log_type)
> There are 3 events as log_type.
>
> I naively tried
> SELECT user_name, log_type_fk, COUNT(log_type_fk)
> FROM log
> JOIN users ON (user_id = user_fk)
> WHERE (ts IS BETWEEN sometime AND another)
> GROUP BY user_name, log_type_fk
> ORDER BY user_name, log_type_fk
>
> This results e.g. to
>
> user1, type1, 2
> user1, type2, 3
> user1, type3, 7
> user2, type1, 11
> user2, type3, 17
>
> but I needed also
> user2, type2, 0
>
> How would I get there ?

without the WHERE-condition:

test=*# select * from log;
log_id | log_type_fk | user_fk | ts
--------+-------------+---------+---------------------
1 | 1 | 1 | 2009-07-23 00:00:00
2 | 2 | 2 | 2009-07-23 00:00:00
(2 rows)

test=*# select * from users;
user_id | user_name
---------+-----------
1 | user1
2 | user2
(2 rows)

test=*# select * from log_type;
log_type_id | log_type
-------------+----------
1 | type1
2 | type2
(2 rows)

test=*# select foo.user_name, foo.log_type, sum(case when log_type_fk is
not null then 1 else 0 end) from (select user_id, user_name,
log_type_id, log_type from users cross join log_type) foo full join log
on ((foo.user_id, foo.log_type_id)=(log.user_fk, log.log_type_fk)) group
by 1,2 order by 1,2;
user_name | log_type | sum
-----------+----------+-----
user1 | type1 | 1
user1 | type2 | 0
user2 | type1 | 0
user2 | type2 | 1
(4 rows)

HTH, Andreas
--
Andreas Kretschmer
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