Creating an aggregate function

Hi all,

This e-mail is long because I am providing lots of details on the
problem. It's an OpenACS module that we are porting so it'll have lots
of users, you can be sure.

I have this view that I am porting that is a UNION of two self OUTER
JOINed views. PG does not support UNIONs in views, so we thought of
creating our own aggregate functions to do the job.

There are no examples for CREATE AGGREGATE in the docs, but we made it
work, at least partially, but it explodes a little after the first row
column.

Here's the original Oracle query:

create or replace view cs_n_sessions_day_user as
select b.date_id, b.n_sessions_day, nvl(a.n_users, 0) as members,
b.n_users as non_members
from cs_historical_visits_grouped a,cs_historical_visits_grouped b
where b.n_sessions_day = a.n_sessions_day(+)
and b.date_id = a.date_id(+)
and 1 = a.member_p(+)
and b.member_p = 0
UNION
select a.date_id, a.n_sessions_day, a.n_users as members,
nvl(b.n_users, 0) as non_members
from cs_historical_visits_grouped a, cs_historical_visits_grouped b
where a.n_sessions_day = b.n_sessions_day(+)
and a.date_id = b.date_id(+)
and a.member_p = 1
and 0 = b.member_p(+);
Here is our port of the cs_historical_visits_grouped view:

create view cs_historical_visits_grouped as
select date_id, n_sessions_day, not_null_integer_p(user_id) as
member_p, count(browser_id) as n_users
from cs_historical_visits
group by date_id, n_sessions_day;

not_null_integer_p is a function we created that basically does case
when user_id is null then 1 else 0 end, but for some reason PG wouldn't
take it in a view.

Here's a helper view for our aggregate function:

create view cs_hist_visits_grouped_txt as
select date_id, n_sessions_day, member_p, n_users,
member_p::varchar || ' ' || n_users::varchar as
member_p_n_users
from cs_historical_visits_grouped;

And here are the aggregate functions:

create function agg_if_member (integer, varchar)
returns integer as '
declare
a_int alias for $1;
a_varchar alias for $2;
member_p integer;
num_members integer;
begin
member_p := substr(a_varchar, 1, 1)::integer;
num_members := substr(a_varchar, 3)::integer;
if member_p = 1 then
return num_members;
else
return a_int;
end if;
end;
' language 'plpgsql';

create function agg_if_not_member (integer, varchar)
returns integer as '
declare
a_int alias for $1;
a_varchar alias for $2;
return_val integer;
member_p integer;
num_members integer;
begin
member_p := substr(a_varchar, 1, 1)::integer;
num_members := substr(a_varchar, 3)::integer;
return_val := 0;
if a_int is not null then
return_val := a_int;
end if;
if member_p = 0 and num_members > a_int then
return_val := num_members;
end if;
return return_val;
end;
' language 'plpgsql';

create aggregate num_members_or_zero (
basetype = varchar,
stype1 = integer,
sfunc1 = agg_if_member,
initcond1 = 0);

create aggregate num_non_members_or_zero (
basetype = varchar,
stype1 = integer,
sfunc1 = agg_if_not_member,
initcond1 = 0);

and our query was:

select date_id, n_sessions_day,
num_members_or_zero(member_p_n_users) as members,
num_non_members_or_zero(member_p_n_users) as non_members
from foobar
group by date_id, n_sessions_day;

Our fake table foobar had the same structure as our cs_hist_grouped_txt
view has, and this was the dummy data we had inserted to
play with:

date_id | n_sessions_day | member_p | n_users | member_p_n_users
---------+----------------+----------+---------+------------------
1 | 500 | 0 | 50 | 0 50
1 | 500 | 1 | 30 | 1 30
2 | 2000 | 1 | 210 | 1 210
2 | 2000 | 0 | 999 | 0 999

and our output was:

date_id | n_sessions_day | members | non_members
---------+----------------+-----------+-------------
1 | 500 | 30 | 136394044
2 | 2000 | 136394612 | 136394612

the values for members is what we expected for date_id == 1, but the
other ones are all goofy. Anybody has any ideas or worked with CREATE
AGGREGATE before?

Sorry about the long email and TIA.

-Roberto Mello
--
Roberto Mello, rmello(at)cc(dot)usu(dot)edu - GNU/Linux Reg.User #96240
Computer Science - Utah State University
USU Free Software and GNU/Linux Club, President
http://fslc.usu.edu - http://www.brasileiro.net/roberto