Thanks Robin.

The problem with this is that the result I get is not correct.
I don't know why but it is not equivalent to this: SELECT MIN(o_id) FROM (SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333) AS s;

Here 's how managed to make it work (and seems to have better execution time):

CREATE LOCAL TEMPORARY TABLE latestorders AS SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333 WITH DATA ON COMMIT PRESERVE ROWS;

DECLARE min_o_id int;
SET min_o_id = (SELECT MIN(o_id) FROM latestorders);

SELECT i_id, i_title, a_fname, a_lname
FROM item, author, order_line
WHERE ol_o_id > min_o_id
AND i_id = ol_i_id AND i_a_id = a_id AND i_subject = 'HOME'
GROUP BY i_id, i_title, a_fname, a_lname
ORDER BY SUM(ol_qty) DESC
LIMIT 50;

Embedding the query to the WHERE clause to avoid the intermediate variable doesn't work. I simply don't get any response (result or error) from the system.


On Wed, Jul 2, 2014 at 9:17 AM, Robin Cijvat <robin.cijvat@monetdbsolutions.com> wrote:
In my previous query, I forgot to give the biggest subquery an alias. So the query will become something like this:


SELECT MIN(o_id)
FROM (
    SELECT o_id
    FROM (
        SELECT row_number() over (ORDER BY o_date DESC) as row, o_id
        FROM orders
    ) AS sub
    WHERE sub.row <= 3333
) sub2;



On 02-07-14 09:15, Robin Cijvat wrote:
Hi Dimitris (sorry for the typo),

@Bryan: Thanks for mentioning that, I was not aware of the windowing functionality :) I tried it out, and for me it seems to work. So for your simple example, you would do the following rewrite:

SELECT MIN(o_id) FROM (SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333) AS s;

-->

SELECT MIN(o_id)
FROM (
    SELECT o_id
    FROM (
        SELECT row_number() over (ORDER BY o_date DESC) as row, o_id
        FROM orders
    ) AS sub
    WHERE sub.row <= 3333
);

I had to add an extra subquery, since the WHERE clause in the part where you select the row_number(), is not aware of the identifier 'row' yet.

I would advise using this over the temporary tables, since a) it is much simpler to write and b) you don't have to worry about having to manage intermediate results yourself.

I hope you can extend this example to your original query.

Best,
Robin





On 01-07-14 20:43, Bryan Senseman wrote:

Actually, I think you can trick it depending on your version of MonetDB and use the RANK windowing function inside the innermost subquery and then use a standard where clause on the appropriate outside snippet to limit the returned rows.

 

Bryan

From: users-list [mailto:users-list-bounces+monetdb=openbi.com@monetdb.org] On Behalf Of Dimitris Karampinas
Sent: Tuesday, July 01, 2014 2:27 PM
To: Communication channel for MonetDB users
Subject: Re: MonetDB and cpu resources management

 

DimitrIs :)

 

I thought of temporary tables before posting but a) I was skeptic about the extra overhead b) my first try to use them failed...

 

For the aforementioned query I do the following:

 

CREATE LOCAL TEMPORARY TABLE toporders AS SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333 WITH DATA ON COMMIT PRESERVE ROWS;

 

SELECT i_id, i_title, a_fname, a_lname

FROM item, author, order_line

WHERE ol_o_id > (SELECT MIN(o_id) FROM toporders)

            AND i_id = ol_i_id AND i_a_id = a_id AND i_subject = 'HOME'

GROUP BY i_id, i_title, a_fname, a_lname

ORDER BY SUM(ol_qty) DESC

LIMIT 50;

 

 

The command prompt returns but there is no result, neither any syntax/whatever error response.

 

Cheers!

Dimitris

 

On Tue, Jul 1, 2014 at 5:29 PM, Robin Cijvat <robin.cijvat@monetdbsolutions.com> wrote:

Hi Dimitras.

MonetDB indeed does not support LIMIT in subqueries. A simple workaround is just storing the result of the subquery in a temporary table (https://www.monetdb.org/Documentation/Manuals/SQLreference/Tables) and then referring to this temporary table in the main query.

Maybe not an ideal solution, but it will work.

Regards,
Robin Cijvat



On 01-07-14 16:53, Dimitris Karampinas wrote:

Hi,

 

Thanks for your answers. I hope stethoscope will help.

 

One more question, not relevant to the previous one but I hope it's OK not to open a new thread.

 

I'm trying to run the BestSellers query from TPC-W on MonetDB.

The query works as follows:

- Take the smallest order id from the most recent 3333 orders.

- Then take all order lines more recent than that, sum their quantities by item, and display the top 50 by total quantity.

 

Here is some SQL code for this:

 

SELECT i_id, 

       i_title, 

       a_fname, 

       a_lname 

FROM   item, 

       author, 

       order_line 

WHERE  ol_o_id > (SELECT Min(o_id) 

                  FROM   (SELECT o_id 

                          FROM   orders 

                          ORDER  BY o_date DESC 

                          LIMIT  3333) s) 

       AND i_id = ol_i_id 

       AND i_a_id = a_id 

       AND i_subject = 'HOME' 

GROUP  BY i_id, 

          i_title, 

          a_fname, 

          a_lname 

ORDER  BY Sum(ol_qty) DESC 

LIMIT  50;

 

 

I'm having trouble in expressing the nested sub-query:

 

SELECT MIN(o_id) FROM (SELECT o_id FROM orders ORDER BY o_date DESC LIMIT 3333) AS s;

 

Searching in previous mails in this list, I found out that MonetDB does not support ORDER BY or LIMIT in subqueries.

Is there any workaround ?

 

 

Cheers!

Dimitris

 

On Mon, Jun 30, 2014 at 2:24 PM, Sjoerd Mullender <sjoerd@acm.org> wrote:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1


On 2014-06-30 11:53, Dimitris Karampinas wrote:
> Hi,
>
> I'm trying to set the maximum number of cores using gdk_nr_threads
> parameter but it doesn't seem to work for me. I've tried "variants"
> of this command: monetdbd set gdk_nr_threads=4 start /my/dbfarm but
> it seems like gdk_nr_threads is not a supported property.
>
> Additionally to this, I would like to ask how does MonetDB handle
> concurrent user sessions and the available cpu resources ? The
> manual says there is support for "inter- and intra- parallelism".
> Can someone roughly explain me what to expect or give me a pointer
> to the code that is responsible for resource management ?
>
> Cheers! Dimitris

Read the manual: man monetdb.  It will tell you about the
nthreads=number command.


- --
Sjoerd Mullender
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

iQCVAwUBU7FW4T7g04AjvIQpAQKNnQP/STLE1LROqd1bixEDOXRkFt2C8UtbPAMo
WlohnW7z7xEis9EziIq/rEOV8n/xnnyhiZG6YENoL+faB3UbM2OIHCr7UgZqL3hH
VlpsB0NIztt6XRT/Ax+MlwwYf9pOGefbDi6PlHzNkitBVfah/H6ws613oiAD1/lZ
ElMs8AQ0m28=
=iDi8
-----END PGP SIGNATURE-----

_______________________________________________
users-list mailing list
users-list@monetdb.org
https://www.monetdb.org/mailman/listinfo/users-list

 

 

_______________________________________________
users-list mailing list
users-list@monetdb.org
https://www.monetdb.org/mailman/listinfo/users-list

 


_______________________________________________
users-list mailing list
users-list@monetdb.org
https://www.monetdb.org/mailman/listinfo/users-list

 


This transmission is confidential and intended solely for the use of the recipient named above. It may contain confidential, proprietary, or legally privileged information. If you are not the intended recipient, you are hereby notified that any unauthorized review, use, disclosure or distribution is strictly prohibited. If you have received this transmission in error, please contact the sender by reply e-mail and delete the original transmission and all copies from your system.



_______________________________________________
users-list mailing list
users-list@monetdb.org
https://www.monetdb.org/mailman/listinfo/users-list




_______________________________________________
users-list mailing list
users-list@monetdb.org
https://www.monetdb.org/mailman/listinfo/users-list


_______________________________________________
users-list mailing list
users-list@monetdb.org
https://www.monetdb.org/mailman/listinfo/users-list