PL/pgSQL: concatenating row values to a JSON-like string - postgresql

Question

I'm trying to retrieve player statistics for the last 20 weeks:
# select yw, money
from pref_money where id='OK122471020773'
order by yw desc limit 20;
yw | money
---------+-------
2010-52 | 1130
2010-51 | 3848
2010-50 | 4238
2010-49 | 2494
2010-48 | 936
2010-47 | 3453
2010-46 | 3923
2010-45 | 1110
2010-44 | 185
(9 rows)
But I would like to have the result as a string, where all values are concatenated by colons and semicolons like this:
"2010-44:185;2010-45:1110; .... ;2010-52:1130"
So I'm trying to create the following PL/pgSQL procedure:
create or replace function pref_money_stats(_id varchar)
returns varchar as $BODY$
begin
declare stats varchar;
for row in select yw, money from pref_money
where id=_id order by yw desc limit 20 loop
stats := row.id || ':' || row.money || ';' stats;
end loop;
return stats;
end;
$BODY$ language plpgsql;
But I get the syntax error:
ERROR: syntax error at or near "for"
LINE 7: for row in select yw, money from pref_money where id...
Using PostgreSQL 8.4.6 with CentOS 5.5 Linux.
UPDATE:
I'm trying to perform all this string concatenation with PL/pgSQL and not in PHP script, because I already have a main SQL select statement, which returns user information and that information is printed row by row as XML for my mobile app:
select u.id,
u.first_name,
u.female,
u.city,
u.avatar,
m.money,
u.login > u.logout as online
from pref_users u, pref_money m where
m.yw=to_char(current_timestamp, 'YYYY-IW')
and u.id=m.id
order by m.money desc
limit 20 offset ?
Here is the screenshot of the mobile app:
And here is an XML excerpt:
<?xml version="1.0"?>
<pref>
<user id="OK510352632290" name="ирина" money="2067" pos="1" medals="1" female="1" avatar="http://i221.odnoklassniki.ru/getImage?photoId=259607761026&photoType=0" city="староконстантинов" />
<user id="OK19895063121" name="Александр" money="1912" pos="2" online="1" avatar="http://i69.odnoklassniki.ru/getImage?photoId=244173589553&photoType=0" city="Сызрань" />
<user id="OK501875102516" name="Исмаил" money="1608" pos="3" online="1" avatar="http://i102.odnoklassniki.ru/res/stub_128x96.gif" city="Москва" />
.....
</pref>
But my problem is that I have 3 other tables, from which I need that statistics for the last 20 weeks. So I'm hoping to create 3 procedures returning varchars as in my original post and integrate them in this SQL select statement. So that I can add further attributes to the XML data:
<user id="OK12345" .... money_stats="2010-44:185;2010-45:1110; .... ;2010-52:1130" ..... />
Thank you!
Alex

Answer 1

Aggregate functions are good for concatenating values:
create or replace function test
(text, text, text)
returns text as
$$
select $1 || ':' || $2 || ';' || $3
$$
language sql;
drop function test(text, text);
drop aggregate test(text, text) cascade;
create aggregate test(text, text)
(
sfunc = test,
stype = text,
initcond = ''
);
test=# select test(a::text, b::text) from (select generate_series(1,3) as a, generate_series(4,5) a
s b) t;
:1;4:2;5:3;4:1;5:2;4:3;5
(I'll leave it to you to deal with the leading colin :-)

Answer 2

You probably have already found the answer to your problem. Even so, the problem was indeed syntax.
The problem was that the declare statement was misplaced: it should appear before the begin (docs):
create or replace function pref_money_stats(_id varchar)
returns varchar as $BODY$
declare stats varchar;
begin
...
Another detail to take notice of is that you need to declare row as a record:
declare
stats varchar;
row record;
Then this statement will run properly:
for row in select yw, money from pref_money where id=_id order by yw desc limit 20 loop

Answer 3

This is not exactly JSON but pretty close:
SELECT ARRAY
(
SELECT ROW(yw, money)
FROM pref_money
WHERE id = 'OK122471020773'
ORDER BY
yw DESC
LIMIT 20
)::TEXT
This will output this string:
{"(2010-44:185)","(2010-45:1110)",…,"(2010-52:1130)"}
which can later be cast back into the appropriate types.