Re: Concatenating several rows with a semicolon

2010/12/28 Alexander Farber <alexander(dot)farber(at)gmail(dot)com>

> Hello,
>
> I'm working on a small app, which receives a list of 20 players in XML
> format.
>
> The initial version works ok and I use there just 1 SQL statement and thus
> it is easy for me to fetch results row by row and print XML at the same
> time:
>
> select u.id,
> u.first_name,
> 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 ?
>
> My problem is however, that I need to add more data for each user
> representing their statistics over the last 20 weeks.
> And that data is in separate tables: pref_money, pref_pass, pref_game:
>
> # select yw, money
> from pref_money where id='OK122471020773'
> order by yw desc limit 20;
> yw | money
> ---------+-------
> 2010-52 | 760
> 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)
>
SELECT string_agg(yw::text || money::text, ';');

>
> For example for the table above I'd like to concatenate
> those rows and add them as an XML attribute for that user:
>
> <user id="OK122471020773" first_name="..." city="..." ...
> pref_money="2010-52:760;2010-51:3848;2010-50:4238;...." />
>
> so that I can take that attribute in my app and use it in a chart.
>
> My problem is that I don't know how to bring this together
> in 1 SQL statement (i.e. the SQL statement at the top and
> then the concatenated 20 rows from 3 tables).
>
> Is it possible? Maybe I need to write a PgPlSQL
> procedure for each of the 3 tables and then add them
> to the SQL statement above? But how do I concatenate
> the rows, should I create a PgPlSQL variable and always
> append values to it in a loop or is there a better way?
>
> Thank you for any hints
> Alex
>
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--
// Dmitriy.