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:
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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
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