Thread: How to split a table?
Hi,
I want to split a table to 2 small tables. The 1st one contains 60% records which are randomly selected from the source table.
How to do it?
Regards,
Felix
Felix Zhang <felix.zhang.2005@gmail.com> schrieb: > Hi, > > I want to split a table to 2 small tables. The 1st one contains 60% records > which are randomly selected from the source table. > How to do it? Why do you want to do this? Andreas -- Really, I'm not out to destroy Microsoft. That will just be a completely unintentional side effect. (Linus Torvalds) "If I was god, I would recompile penguin with --enable-fly." (unknow) Kaufbach, Saxony, Germany, Europe. N 51.05082°, E 13.56889°
to do some statistics analysis.
2006/10/17, Andreas Kretschmer <akretschmer@spamfence.net>:
Felix Zhang <felix.zhang.2005@gmail.com> schrieb:
> Hi,
>
> I want to split a table to 2 small tables. The 1st one contains 60% records
> which are randomly selected from the source table.
> How to do it?
Why do you want to do this?
Andreas
--
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect. (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly." (unknow)
Kaufbach, Saxony, Germany, Europe. N 51.05082°, E 13.56889°
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am Tue, dem 17.10.2006, um 1:53:35 -0700 mailte Gregory S. Williamson folgendes: > Perhaps something like: > > CREATE TABLE foo2 AS SELECT * FROM foo WHERE (rand() <= 0.60); Then we have 2 tables: one with 100% data and one with around 60% ;-) If the table contains a primary key you can delete simple the copied records from the origin table. (delete from origin where pk in (select pk from copy); > > -----Original Message----- Please, no top-posting with fullquote below. Andreas -- Andreas Kretschmer Kontakt: Heynitz: 035242/47215, D1: 0160/7141639 (mehr: -> Header) GnuPG-ID: 0x3FFF606C, privat 0x7F4584DA http://wwwkeys.de.pgp.net
On Tue, Oct 17, 2006 at 03:39:21PM +0800, Felix Zhang wrote: > I want to split a table to 2 small tables. The 1st one contains 60% > records which are randomly selected from the source table. How to do > it? i do my A/B-Group splitting usually by &1 the serial of the table. assuming, that there are no irregularities in the process of creating your entries, this should give a 50/50 split, which is reuseable for future things and there never is a intersection of the two groups. -- cu
I would do
select * into mynewtable from myoldtable ORDER by random() LIMIT 15000
where 15000 in this case is <your table row count>*.6
If you want to create another table with 40% of the remaining data then something like
select * into mynewtable2 from myoldtable where myoldtable.primarykey NOT IN(select primarykey from mynewtable)
]
In this case primarykey you would replace with the primary key field of your table.
From: pgsql-novice-owner@postgresql.org [mailto:pgsql-novice-owner@postgresql.org] On Behalf Of Felix Zhang
Sent: Tuesday, October 17, 2006 3:39 AM
To: pgsql-sql@postgresql.org; pgsql-general@postgresql.org; pgsql-novice@postgresql.org
Subject: [NOVICE] How to split a table?
Hi,
I want to split a table to 2 small tables. The 1st one contains 60% records which are randomly selected from the source table.
How to do it?
Regards,
Felix
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Perhaps something like:
CREATE TABLE foo2 AS SELECT * FROM foo WHERE (rand() <= 0.60);
?
HTH,
Greg Williamson
DBA
GlobeXplorer LLC
-----Original Message-----
From: pgsql-sql-owner@postgresql.org on behalf of Andreas Kretschmer
Sent: Tue 10/17/2006 1:34 AM
To: pgsql-general@postgresql.org; pgsql-sql@postgresql.org; pgsql-novice@postgresql.org
Cc:
Subject: Re: [SQL] [GENERAL] How to split a table?
Felix Zhang <felix.zhang.2005@gmail.com> schrieb:
> Hi,
>
> I want to split a table to 2 small tables. The 1st one contains 60% records
> which are randomly selected from the source table.
> How to do it?
Why do you want to do this?
Andreas
--
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect. (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly." (unknow)
Kaufbach, Saxony, Germany, Europe. N 51.05082°, E 13.56889°
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A crude approach would be to add a column to the original table; then update that based on the rand() call: update foo set i_am_a_60 = 1 where (rand() <= 0.60); create table foo_60 as select * from foo where i_am_a_60 = 1; create table foo_40 as select * from foo where i_am_a_60 <> 1; The CASE condition might be usable as well but I haven't puzzled it out ... G -----Original Message----- From: pgsql-sql-owner@postgresql.org on behalf of A. Kretschmer Sent: Tue 10/17/2006 2:12 AM To: pgsql-sql@postgresql.org; pgsql-novice@postgresql.org Cc: Subject: Re: [SQL] [GENERAL] How to split a table? am Tue, dem 17.10.2006, um 1:53:35 -0700 mailte Gregory S. Williamson folgendes: > Perhaps something like: > > CREATE TABLE foo2 AS SELECT * FROM foo WHERE (rand() <= 0.60); Then we have 2 tables: one with 100% data and one with around 60% ;-) If the table contains a primary key you can delete simple the copied records from the origin table. (delete from origin where pk in (select pk from copy); > > -----Original Message----- Please, no top-posting with fullquote below. Andreas -- Andreas Kretschmer Kontakt: Heynitz: 035242/47215, D1: 0160/7141639 (mehr: -> Header) GnuPG-ID: 0x3FFF606C, privat 0x7F4584DA http://wwwkeys.de.pgp.net ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings ------------------------------------------------------- Click link below if it is SPAM gsw@globexplorer.com "https://mailscanner.globexplorer.com/dspam/dspam.cgi?signatureID=45349cb0275391789821027&user=gsw@globexplorer.com&retrain=spam&template=history&history_page=1" !DSPAM:45349cb0275391789821027! -------------------------------------------------------
"Gregory S. Williamson" <gsw@globexplorer.com> writes: > A crude approach would be to add a column to the original table; then update > that based on the rand() call: > > update foo set i_am_a_60 = 1 where (rand() <= 0.60); > create table foo_60 as select * from foo where i_am_a_60 = 1; > create table foo_40 as select * from foo where i_am_a_60 <> 1; > > The CASE condition might be usable as well but I haven't puzzled it out ... If he's asking that 60% of the contents of the original table be randomly selected this won't work. He'll have to count how many rows the original table has, then loop randomly selecting rows until he has reached 60% of that total. Otherwise he might end up with something completely different from what he wants. On the other hand if he wants rows whose randomness factor at the time they were looked at was bigger than 0.6 then he can use that rand() trick. -- Jorge Godoy <jgodoy@gmail.com>