Thread: Categories and subcategories : more details
> I have two tables : the first for categories and the second for > subcategories.I want to get a result like Yahoo! For each category , > the sql > query must return maximum 3 subcategories. I can't use "limit" in a > subquery > because I use Postgresql 7.0. Examples : table CATEG : ida categ1 X2 Y3 Z table SUBCATEG : idb subcateg ida 1 x1 1 2 x2 1 3 x3 1 4 x4 1 5 y1 2 6 y2 2 7 z1 3 I 'd like to obtain a table with maximum 2 subcateg per categ : table result : categ subcateg X x1 X x2 Y y1 Y y2 Z z1 any help? Regards, Rachel
Rachel, See below: > Examples : > > table CATEG : > ida categ > 1 X > 2 Y > 3 Z > > table SUBCATEG : > idb subcateg ida > 1 x1 1 > 2 x2 1 > 3 x3 1 > 4 x4 1 > 5 y1 2 > 6 y2 2 > 7 z1 3 > > I 'd like to obtain a table with maximum 2 subcateg per categ : > > table result : > > categ subcateg > X x1 > X x2 > Y y1 > Y y2 > Z z1 > Without LIMIT in subselects, you're in performance hell as far as doing the above is concerned. Frankly, I can't see any way to do it that doesn't involve a PL/pgSQL procedure that generates a temporary table, and has to run once for every row in your result set. I'll post code later if nobody comes up with a better solution. If you knew all of your categories in advance, you could do this via an annoying UNION statement. I'm assuming, however, that it needs to be dynamic. -Josh Berkus -- ______AGLIO DATABASE SOLUTIONS___________________________ Josh Berkus Complete informationtechnology josh@agliodbs.com and data management solutions (415) 565-7293 for law firms, small businesses fax 621-2533 and non-profit organizations. San Francisco
Hi,
I have a problem today when I vacuum one table which is vacuumed every
today, I tried re_create index also, didn't work.
urldb=# VACUUM VERBOSE ANALYZE id;
NOTICE: Vacuum: table not found
VACUUM
urldb=# VACUUM VERBOSE ANALYZE ip;
NOTICE: --Relation ip--
NOTICE: Pages 4373: Changed 0, reaped 151, Empty 0, New 0; Tup 662929:
Vac 164, Keep/VTL 0/0, Crash 0, UnUsed 23401, MinLen 48, MaxLen 48;
Re-using: Free/Avail. Space 1137624/0; EndEmpty/Avail. Pages 150/0. CPU
0.33s/2.28u sec.
NOTICE: Index ip_ip: Pages 2093; Tuples 662929: Deleted 0. CPU
0.15s/0.73u sec.
NOTICE: Index ip_id: Pages 1311; Tuples 662929: Deleted 0. CPU
0.11s/0.70u sec.
NOTICE: Rel ip: Pages: 4373 --> 4223.
NOTICE: FlushRelationBuffers(ip, 4223): block 4365 is referenced (private
0, global 8)
FATAL 1: VACUUM (vc_vacheap): FlushRelationBuffers returned -2
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
any suggestion??
Jie LIANG
St. Bernard Software
10350 Science Center Drive
Suite 100, San Diego, CA 92121
Office:(858)320-4873
jliang@ipinc.com
www.stbernard.com
www.ipinc.com
Jie Liang <jliang@ipinc.com> writes:
> NOTICE: FlushRelationBuffers(ip, 4223): block 4365 is referenced (private
> 0, global 8)
> FATAL 1: VACUUM (vc_vacheap): FlushRelationBuffers returned -2
Try restarting your postmaster.
regards, tom lane
Tom,
NOTICE: --Relation ip--
NOTICE: Pages 4244: Changed 1, reaped 13, Empty 0, New 0; Tup 665627: Vac
32, Keep/VTL 0/0, Crash 0, UnUsed 594, MinLen 48, MaxLen 48; Re-using:
Free/Avail. Space 33168/26016; EndEmpty/Avail. Pages 0/12. CPU 0.32s/2.26u
sec.
NOTICE: Index ip_ip: Pages 3204; Tuples 665627: Deleted 13. CPU
0.20s/0.80u sec.
NOTICE: Index ip_id: Pages 1499; Tuples 665627: Deleted 13. CPU
0.04s/0.81u sec.
NOTICE: Rel ip: Pages: 4244 --> 4240; Tuple(s) moved: 13. CPU 0.00s/0.00u
sec.
NOTICE: Index ip_ip: Pages 3204; Tuples 665627: Deleted 13. CPU
0.19s/0.79u sec.
NOTICE: Index ip_id: Pages 1499; Tuples 665627: Deleted 13. CPU
0.09s/0.74u sec.
NOTICE: FlushRelationBuffers(ip, 4240): block 4242 is referenced (private
0, global 1)
FATAL 1: VACUUM (vc_repair_frag): FlushRelationBuffers returned -2
pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
The connection to the server was lost. Attempting reset: Succeeded.
This happen again today,
urldb=# select version();
version
-------------------------------------------------------------------------
PostgreSQL 7.0.0 on i386-unknown-freebsdelf3.4, compiled by gcc 2.7.2.3
Dose later version such as 7.0.3 resolved this problem??
if so, which version I should install?
Jie LIANG
St. Bernard Software
10350 Science Center Drive
Suite 100, San Diego, CA 92121
Office:(858)320-4873
jliang@ipinc.com
www.stbernard.com
www.ipinc.com
On Tue, 20 Mar 2001, Tom Lane wrote:
> Jie Liang <jliang@ipinc.com> writes:
> > NOTICE: FlushRelationBuffers(ip, 4223): block 4365 is referenced (private
> > 0, global 8)
> > FATAL 1: VACUUM (vc_vacheap): FlushRelationBuffers returned -2
>
> Try restarting your postmaster.
>
> regards, tom lane
>
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Jie Liang <jliang@ipinc.com> writes:
> Dose later version such as 7.0.3 resolved this problem??
Possibly. Try it and see. You should be running 7.0.3 anyway,
just on general principles.
regards, tom lane