Thread: Returning array of IDs as a sub-query with group-by

Returning array of IDs as a sub-query with group-by

From
Andreas Joseph Krogh
Date:
Hi all.
I have the following schema:

create table item(
id serial primary key
);


create table item_log(
id serial primary key,
item_id integer not null references item(id),
price numeric NOT NULL
);


insert into item(id) values(1);
insert into item(id) values(2);
insert into item(id) values(3);
insert into item(id) values(4);

insert into item_log(item_id, price) values(1, 100);
insert into item_log(item_id, price) values(1, 100);
insert into item_log(item_id, price) values(1, 100);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(1, 200);
insert into item_log(item_id, price) values(2, 200);
insert into item_log(item_id, price) values(2, 200);

Now, to get out all log-entries grouped on price with count the following
query gives me what I want

SELECT COUNT(il.price), i.id AS item_id, il.price FROM item i, item_log il
WHERE i.id = il.item_id GROUP BY il.price, i.id;
count | item_id | price
-------+---------+-------    3 |       1 |   100    6 |       1 |   200    2 |       2 |   200
(3 rows)

Now - I would like to return an ARRAY of item_log.id for each of the two rows.
The result I'm looking for would look like this:
count | item_id | price | item_id_array
-------+---------+-------+---------------    3 |       1 |   100 | {1,2,3}    6 |       1 |   200 | {4,5,6,7,8,9}    2
|      2 |   200 | {10,11} 

I tried this query which complains about an ungruoped column:

SELECT COUNT(il.price), i.id AS item_id, il.price,ARRAY(SELECT a.id FROM item_log a WHERE a.id = il.id) AS
item_id_arrayFROM item i, item_log il WHERE i.id = il.item_id GROUP BY il.price, i.id; 

ERROR:  subquery uses ungrouped column "il.id" from outer query

Any hints?

--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
------------------------+---------------------------------------------+
OfficeNet AS            | The most difficult thing in the world is to |
Karenslyst Allé 11      | know how to do a thing and to watch         |
PO. Box 529 Skøyen      | somebody else doing it wrong, without       |
0214 Oslo               | comment.                                    |
NORWAY                  |                                             |
Tlf:    +47 24 15 38 90 |                                             |
Fax:    +47 24 15 38 91 |                                             |
Mobile: +47 909  56 963 |                                             |
------------------------+---------------------------------------------+


Re: Returning array of IDs as a sub-query with group-by

From
Andreas Joseph Krogh
Date:
On Saturday 25 August 2007 17:10:57 Andreas Joseph Krogh wrote:
> Hi all.
> I have the following schema:
>
> create table item(
> id serial primary key
> );
>
>
> create table item_log(
> id serial primary key,
> item_id integer not null references item(id),
> price numeric NOT NULL
> );
>
>
> insert into item(id) values(1);
> insert into item(id) values(2);
> insert into item(id) values(3);
> insert into item(id) values(4);
>
> insert into item_log(item_id, price) values(1, 100);
> insert into item_log(item_id, price) values(1, 100);
> insert into item_log(item_id, price) values(1, 100);
> insert into item_log(item_id, price) values(1, 200);
> insert into item_log(item_id, price) values(1, 200);
> insert into item_log(item_id, price) values(1, 200);
> insert into item_log(item_id, price) values(1, 200);
> insert into item_log(item_id, price) values(1, 200);
> insert into item_log(item_id, price) values(1, 200);
> insert into item_log(item_id, price) values(2, 200);
> insert into item_log(item_id, price) values(2, 200);
>
> Now, to get out all log-entries grouped on price with count the following
> query gives me what I want
>
> SELECT COUNT(il.price), i.id AS item_id, il.price FROM item i, item_log il
> WHERE i.id = il.item_id GROUP BY il.price, i.id;
>
>  count | item_id | price
> -------+---------+-------
>      3 |       1 |   100
>      6 |       1 |   200
>      2 |       2 |   200
> (3 rows)
>
> Now - I would like to return an ARRAY of item_log.id for each of the two
> rows. The result I'm looking for would look like this:
>
>  count | item_id | price | item_id_array
> -------+---------+-------+---------------
>      3 |       1 |   100 | {1,2,3}
>      6 |       1 |   200 | {4,5,6,7,8,9}
>      2 |       2 |   200 | {10,11}
>
> I tried this query which complains about an ungruoped column:
>
> SELECT COUNT(il.price), i.id AS item_id, il.price,
>  ARRAY(SELECT a.id FROM item_log a WHERE a.id = il.id) AS item_id_array
>   FROM item i, item_log il WHERE i.id = il.item_id GROUP BY il.price, i.id;
>
> ERROR:  subquery uses ungrouped column "il.id" from outer query
>
> Any hints?

I found the following CREATE AGGREGATE suggestion in the PG-docs:

CREATE AGGREGATE array_accum (anyelement)
(   sfunc = array_append,   stype = anyarray,   initcond = '{}'
);

With this I can easily issue:
SELECT COUNT(il.price), i.id AS item_id, il.price,array_accum(il.id) AS item_id_array FROM item i, item_log il WHERE
i.id= il.item_id GROUP BY il.price, i.id; 

Which does what I want:count | item_id | price | item_id_array
-------+---------+-------+---------------    3 |       1 |   100 | {1,2,3}    6 |       1 |   200 | {4,5,6,7,8,9}    2
|      2 |   200 | {10,11} 
(3 rows)

If someone knows of a way without introducing a new AGGREGATE I'm still
interrested.

--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
------------------------+---------------------------------------------+
OfficeNet AS            | The most difficult thing in the world is to |
Karenslyst Allé 11      | know how to do a thing and to watch         |
PO. Box 529 Skøyen      | somebody else doing it wrong, without       |
0214 Oslo               | comment.                                    |
NORWAY                  |                                             |
Tlf:    +47 24 15 38 90 |                                             |
Fax:    +47 24 15 38 91 |                                             |
Mobile: +47 909  56 963 |                                             |
------------------------+---------------------------------------------+


Re: Returning array of IDs as a sub-query with group-by

From
Ragnar
Date:
On lau, 2007-08-25 at 17:55 +0200, Andreas Joseph Krogh wrote:
> On Saturday 25 August 2007 17:10:57 Andreas Joseph Krogh wrote:

[snip]

> >  count | item_id | price | item_id_array
> > -------+---------+-------+---------------
> >      3 |       1 |   100 | {1,2,3}
> >      6 |       1 |   200 | {4,5,6,7,8,9}
> >      2 |       2 |   200 | {10,11}
> >
> > I tried this query which complains about an ungruoped column:
> >
> > SELECT COUNT(il.price), i.id AS item_id, il.price,
> >  ARRAY(SELECT a.id FROM item_log a WHERE a.id = il.id) AS item_id_array
> >   FROM item i, item_log il WHERE i.id = il.item_id GROUP BY il.price, i.id;
> >
> > ERROR:  subquery uses ungrouped column "il.id" from outer query
> >
> > Any hints?
> 
> I found the following CREATE AGGREGATE suggestion in the PG-docs:

[aggregate solution snipped]

> If someone knows of a way without introducing a new AGGREGATE I'm still 
> interrested.

you can allways do the ARRAY(SELECT...) outside the grouping:
# select *,(select ARRAY(                        SELECT a.id                         FROM item_log as a
       WHERE foo.item_id=a.item_id                              AND foo.price=a.price                        )
)AS item_id_array 
 
from (      select count(*),item_id, price       from item_log       group by item_id, price    ) as foo;
count | item_id | price | item_id_array 
-------+---------+-------+---------------    3 |       1 |   100 | {1,2,3}    6 |       1 |   200 | {4,5,6,7,8,9}    2
|      2 |   200 | {10,11}
 
(3 rows)


but i suspect the aggregate will perform better

gnari




Re: Returning array of IDs as a sub-query with group-by

From
Andreas Joseph Krogh
Date:
On Saturday 25 August 2007 23:02:19 Ragnar wrote:
> On lau, 2007-08-25 at 17:55 +0200, Andreas Joseph Krogh wrote:
> > On Saturday 25 August 2007 17:10:57 Andreas Joseph Krogh wrote:
>
> [snip]
>
> > >  count | item_id | price | item_id_array
> > > -------+---------+-------+---------------
> > >      3 |       1 |   100 | {1,2,3}
> > >      6 |       1 |   200 | {4,5,6,7,8,9}
> > >      2 |       2 |   200 | {10,11}
> > >
> > > I tried this query which complains about an ungruoped column:
> > >
> > > SELECT COUNT(il.price), i.id AS item_id, il.price,
> > >  ARRAY(SELECT a.id FROM item_log a WHERE a.id = il.id) AS item_id_array
> > >   FROM item i, item_log il WHERE i.id = il.item_id GROUP BY il.price,
> > > i.id;
> > >
> > > ERROR:  subquery uses ungrouped column "il.id" from outer query
> > >
> > > Any hints?
> >
> > I found the following CREATE AGGREGATE suggestion in the PG-docs:
>
> [aggregate solution snipped]
>
> > If someone knows of a way without introducing a new AGGREGATE I'm still
> > interrested.
>
> you can allways do the ARRAY(SELECT...) outside the grouping:
> # select *,(select ARRAY(
>                          SELECT a.id
>                          FROM item_log as a
>                          WHERE foo.item_id=a.item_id
>                                AND foo.price=a.price
>                          )
>            ) AS item_id_array
> from (
>        select count(*),item_id, price
>        from item_log
>        group by item_id, price
>      ) as foo;
>
>  count | item_id | price | item_id_array
> -------+---------+-------+---------------
>      3 |       1 |   100 | {1,2,3}
>      6 |       1 |   200 | {4,5,6,7,8,9}
>      2 |       2 |   200 | {10,11}
> (3 rows)
>
>
> but i suspect the aggregate will perform better
>
> gnari

Ok, thanks.

--
Andreas Joseph Krogh <andreak@officenet.no>
Senior Software Developer / Manager
------------------------+---------------------------------------------+
OfficeNet AS            | The most difficult thing in the world is to |
Karenslyst Allé 11      | know how to do a thing and to watch         |
PO. Box 529 Skøyen      | somebody else doing it wrong, without       |
0214 Oslo               | comment.                                    |
NORWAY                  |                                             |
Tlf:    +47 24 15 38 90 |                                             |
Fax:    +47 24 15 38 91 |                                             |
Mobile: +47 909  56 963 |                                             |
------------------------+---------------------------------------------+