Обсуждение: ordered by join? ranked aggregate? how to?

What I need is to join 2 tables

CREATE TABLE master(   id INT4
);


CREATE TABLE slave (   master_id INT4,   rank INT4,   value TEXT);


What I need is to make the query:

SELECT m.id, array_agg(s.value) AS my_problematic_array
FROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id)
GROUP BY m.id;

return the 'my_problematic_array' in order specified by slave.rank

As you probably can guest I don't have any idea know how to do it :/

In response to wstrzalka :
> What I need is to join 2 tables
> 
> CREATE TABLE master(
>     id INT4
> );
> 
> 
> CREATE TABLE slave (
>     master_id INT4,
>     rank INT4,
>     value TEXT);
> 
> 
> What I need is to make the query:
> 
> SELECT m.id, array_agg(s.value) AS my_problematic_array
> FROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id)
> GROUP BY m.id;
> 
> return the 'my_problematic_array' in order specified by slave.rank
> 
> As you probably can guest I don't have any idea know how to do it :/

test=*# select * from master;id
---- 1 2
(2 rows)

test=*# select * from slave;master_id | rank | value
-----------+------+-------        1 |    5 | 5        1 |    3 | 3        1 |    7 | 7
(3 rows)

test=*# 
select id, array_agg(unnest) from ( select id, unnest(my_problematic_array) from (   SELECT m.id, array_agg(s.value) AS
my_problematic_arrayFROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id) GROUP BY m.id ) foo order by 1,2
 
) bar group by 1;id | array_agg
----+----------- 1 | {3,5,7} 2 | {NULL}
(2 rows)


Andreas
-- 
Andreas Kretschmer
Kontakt:  Heynitz: 035242/47150,   D1: 0160/7141639 (mehr: -> Header)

In response to wstrzalka :
> What I need is to join 2 tables
> 
> CREATE TABLE master(
>     id INT4
> );
> 
> 
> CREATE TABLE slave (
>     master_id INT4,
>     rank INT4,
>     value TEXT);
> 
> 
> What I need is to make the query:
> 
> SELECT m.id, array_agg(s.value) AS my_problematic_array
> FROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id)
> GROUP BY m.id;

Faster solution (compared to my other email):

test=# select id, array_agg(value) from (SELECT m.id, s.value FROM
master AS m LEFT JOIN slave AS s ON (m.id = s.master_id) order by 1,2)
foo group by 1;id | array_agg
----+----------- 1 | {3,5,7} 2 | {NULL}
(2 rows)

Andreas
-- 
Andreas Kretschmer
Kontakt:  Heynitz: 035242/47150,   D1: 0160/7141639 (mehr: -> Header)

On 15 Wrz, 09:56, andreas.kretsch...@schollglas.com ("A. Kretschmer")
wrote:
> In response to wstrzalka :
>
>
>
> > What I need is to join 2 tables
>
> > CREATE TABLE master(
> >     id INT4
> > );
>
> > CREATE TABLE slave (
> >     master_id INT4,
> >     rank INT4,
> >     value TEXT);
>
> > What I need is to make the query:
>
> > SELECT m.id, array_agg(s.value) AS my_problematic_array
> > FROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id)
> > GROUP BY m.id;
>
> Faster solution (compared to my other email):
>
> test=# select id, array_agg(value) from (SELECT m.id, s.value FROM
> master AS m LEFT JOIN slave AS s ON (m.id = s.master_id) order by 1,2)
> foo group by 1;
>  id | array_agg
> ----+-----------
>   1 | {3,5,7}
>   2 | {NULL}
> (2 rows)
>
> Andreas
> --
> Andreas Kretschmer
> Kontakt:  Heynitz: 035242/47150,   D1: 0160/7141639 (mehr: -> Header)
>
> --
> Sent via pgsql-sql mailing list (pgsql-...@postgresql.org)
> To make changes to your subscription:http://www.postgresql.org/mailpref/pgsql-sql


Yes. And No :)

The problem is that in original query the aggregate can be used more
then once :/

So in fact it's like:

SELECT m.id, array_agg(s1.value), array_agg(s2.value)
FROM master AS m LEFT JOIN slave AS s1 ON (m.id = s1.master_id AND
SOME_CONDITION_ON_S1)                              LEFT JOIN slave AS s2 ON (m.id =
s2.master_id AND SOME_OTHER_CONDITION_ON_S1)
GROUP BY m.id;

On 15 Wrz, 10:10, wstrzalka <wstrza...@gmail.com> wrote:
> On 15 Wrz, 09:56, andreas.kretsch...@schollglas.com ("A. Kretschmer")
> wrote:
>
>
>
> > In response to wstrzalka :
>
> > > What I need is to join 2 tables
>
> > > CREATE TABLE master(
> > >     id INT4
> > > );
>
> > > CREATE TABLE slave (
> > >     master_id INT4,
> > >     rank INT4,
> > >     value TEXT);
>
> > > What I need is to make the query:
>
> > > SELECT m.id, array_agg(s.value) AS my_problematic_array
> > > FROM master AS m LEFT JOIN slave AS s ON (m.id = s.master_id)
> > > GROUP BY m.id;
>
> > Faster solution (compared to my other email):
>
> > test=# select id, array_agg(value) from (SELECT m.id, s.value FROM
> > master AS m LEFT JOIN slave AS s ON (m.id = s.master_id) order by 1,2)
> > foo group by 1;
> >  id | array_agg
> > ----+-----------
> >   1 | {3,5,7}
> >   2 | {NULL}
> > (2 rows)
>
> > Andreas
> > --
> > Andreas Kretschmer
> > Kontakt:  Heynitz: 035242/47150,   D1: 0160/7141639 (mehr: -> Header)
>
> > --
> > Sent via pgsql-sql mailing list (pgsql-...@postgresql.org)
> > To make changes to your subscription:http://www.postgresql.org/mailpref/pgsql-sql
>
> Yes. And No :)
>
> The problem is that in original query the aggregate can be used more
> then once :/
>
> So in fact it's like:
>
> SELECT m.id, array_agg(s1.value), array_agg(s2.value)
> FROM master AS m LEFT JOIN slave AS s1 ON (m.id = s1.master_id AND
> SOME_CONDITION_ON_S1)
>                                LEFT JOIN slave AS s2 ON (m.id =
> s2.master_id AND SOME_OTHER_CONDITION_ON_S1)
> GROUP BY m.id;

However it still may work as the order by is the same :) Will try ...