Re: Need magical advice for counting NOTHING

On Thu, Jul 23, 2009 at 1:01 AM, Andreas<maps(dot)on(at)gmx(dot)net> wrote:
> 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

create table users (user_id integer, user_name varchar);
create table log_type (log_type_id integer, log_type integer);
create table log (log_id integer, log_type_fk integer, user_fk integer);
insert into log_type (log_type_id, log_type) values (1, 1);
insert into log_type (log_type_id, log_type) values (2, 2);
insert into users (user_id, user_name) values (1, 'a');
insert into users (user_id, user_name) values (2, 'b');
insert into log (log_id, log_type_fk, user_fk) values (1, 1, 1);
insert into log (log_id, log_type_fk, user_fk) values (2, 2, 1);
insert into log (log_id, log_type_fk, user_fk) values (3, 2, 1);
insert into log (log_id, log_type_fk, user_fk) values (4, 1, 2);

SELECT user_name, log_type.log_type, sum((log_type_fk IS NOT
NULL)::integer) AS count
FROM users JOIN log_type ON (true) LEFT JOIN log ON (user_id = user_fk
AND log.log_type_fk = log_type.log_type)
GROUP BY user_name, log_type.log_type
ORDER BY user_name, log_type.log_type;

user_name | log_type | count
-----------+----------+-------
a | 1 | 1
a | 2 | 2
a | 3 | 0
b | 1 | 1
b | 2 | 0
b | 3 | 0

--
Glenn Maynard