query on query

On Fri, Jul 5, 2013 at 5:09 AM, Jayadevan M
<jayadevan.maymala@ibsplc.com> wrote:

So each student may get counted many times, someone with 99 will be counted
10 times. Possible to do this with a fat query? The table will have many
thousands of records.

Not sure I got the point, but I guess this is a good candidate for a CTE:

WITH RECURSIVE t(n) AS (
VALUES (10)
UNION ALL
SELECT n+10 FROM t WHERE n < 50
)
select count(*), t.n from m, t where mark > t.n group by t.n;

Luca

--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general

So each student may get counted many times, someone with 99 will be
counted
10 times. Possible to do this with a fat query? The table will have
many thousands of records.

Not sure I got the point, but I guess this is a good candidate for a CTE:

WITH RECURSIVE t(n) AS (
VALUES (10)
UNION ALL
SELECT n+10 FROM t WHERE n < 50
)
select count(*), t.n from m, t where mark > t.n group by t.n;

I meant 'fast', not 'fat. Sorry for the typo.

You got it right. The query gets the data exactly as I wanted it. Thanks a lot.

Regards,
Jayadevan

DISCLAIMER: "The information in this e-mail and any attachment is intended only for the person to whom it is addressed and may contain confidential and/or privileged material. If you have received this e-mail in error, kindly contact the sender and destroy all copies of the original communication. IBS makes no warranty, express or implied, nor guarantees the accuracy, adequacy or completeness of the information contained in this email or any attachment and is not liable for any errors, defects, omissions, viruses or for resultant loss or damage, if any, direct or indirect."

--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general

On Fri, Jul 05, 2013 at 08:35:22AM +0200, Luca Ferrari wrote:

On Fri, Jul 5, 2013 at 5:09 AM, Jayadevan M
<jayadevan.maymala@ibsplc.com> wrote:

So each student may get counted many times, someone with 99 will be counted
10 times. Possible to do this with a fat query? The table will have many
thousands of records.

Not sure I got the point, but I guess this is a good candidate for a CTE:

WITH RECURSIVE t(n) AS (
VALUES (10)
UNION ALL
SELECT n+10 FROM t WHERE n < 50
)
select count(*), t.n from m, t where mark > t.n group by t.n;

This might get expensive with many rows.

On the other hand, you can do it like this:

create table grades (username text, grade int4);
insert into grades select 'x', int(rand() * 50) from generate_series(1,100);

with a as
(select (grade/10)*10 as mark,
count(*)
from grades
group by mark)
select mark,
sum(count) over (
order by mark)
from a
order by mark;

Whis should be faster.

Best regards,

depesz

--
Sent via pgsql-general mailing list (pgsql-general@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-general