Thread: Deleting obsolete values

Deleting obsolete values

From

Haller Christoph

Date:

16 October 2001, 17:45:45

This may look familiar to you - it was on the list last month. 
Consider the following table 
create table partitur(userid text, val integer, ts timestamp DEFAULT NOW() );
Do some inserts 
insert into partitur values('Bart', 1440);
insert into partitur values('Lisa', 1024);
insert into partitur values('Bart', 7616);
insert into partitur values('Lisa', 3760);
insert into partitur values('Bart', 3760);
insert into partitur values('Lisa', 7616);
To retrieve the latest values (meaning the last ones inserted) 
Tom Lane wrote 
>This is what SELECT DISTINCT ON was invented for.  I don't know any
>comparably easy way to do it in standard SQL, but with DISTINCT ON
>it's not hard:
>SELECT DISTINCT ON (userid) userid, val, ts FROM partitur
>ORDER BY userid, ts DESC;

My question now is 
Is there a way to delete all rows the select statement did not 
bring up? 
After that *unknown* delete statement 
select userid, val, ts from partitur ;
should show exactly the same as the SELECT DISTINCT ON (userid) ... 
did before. 

Regards, Christoph

Re: Deleting obsolete values

From

"Henshall, Stuart - WCP"

Date:

18 October 2001, 12:50:32

DELETE FROM partitur WHERE EXISTS (SELECT * FROM partitur AS ss_partitur
WHERE ss_partitur.userid=partitur.userid AND ss_partitur.ts>partitur.ts);
Seems like it should seems like it should delete all old values (however I
have not tested it)
- Stuart

> -----Original Message-----
> From:    Haller Christoph [SMTP:ch@rodos.fzk.de]
> Sent:    Tuesday, October 16, 2001 5:45 PM
> To:    pgsql-sql@postgresql.org
> Subject:    Deleting obsolete values
> 
> This may look familiar to you - it was on the list last month. 
> Consider the following table 
> create table partitur
>  (userid text, val integer, ts timestamp DEFAULT NOW() );
> Do some inserts 
> insert into partitur values('Bart', 1440);
> insert into partitur values('Lisa', 1024);
> insert into partitur values('Bart', 7616);
> insert into partitur values('Lisa', 3760);
> insert into partitur values('Bart', 3760);
> insert into partitur values('Lisa', 7616);
> To retrieve the latest values (meaning the last ones inserted) 
> Tom Lane wrote 
> >This is what SELECT DISTINCT ON was invented for.  I don't know any
> >comparably easy way to do it in standard SQL, but with DISTINCT ON
> >it's not hard:
> >SELECT DISTINCT ON (userid) userid, val, ts FROM partitur
> >ORDER BY userid, ts DESC;
> 
> My question now is 
> Is there a way to delete all rows the select statement did not 
> bring up? 
> After that *unknown* delete statement 
> select userid, val, ts from partitur ;
> should show exactly the same as the SELECT DISTINCT ON (userid) ... 
> did before. 
> 
> Regards, Christoph

Doing a regexp-based search/replace?

From

Steve Frampton

Date:

18 October 2001, 15:23:14

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

Hello:

I've got a table containing property_id's with values of the form
###-####.  I would like to discard the slash onwards (and I can't use a
substr() because I am not guaranteed if a) the -#### portion exists, b)
what position it exists from.

If this were a text file, I would use a sed expression such as:

cat textfile | sed 's/-.*$//'

I've been looking for a way to do this with PostgreSQL but so far haven't
found a function that seems to be suitable.  I thought maybe I could do it
with translate, but translate doesn't appear to work with regular
expressions.  So far I've tried things like:

select translate(property_id, '-.*', '') from mytable;

I need to do this, because the -.* portion of my property_id was entered
in error, and I would like to do an update on the entire table and just
have the left-hand side of the property_id column remaining.

Any ideas?  Thank you in advance.

- ---------------< LINUX: The choice of a GNU generation. >-------------
Steve Frampton   <frampton@LinuxNinja.com>   http://www.LinuxNinja.com
GNU Privacy Guard ID: D055EBC5  (see http://www.gnupg.org for details)
GNU-PG Fingerprint: EEFB F03D 29B6 07E8 AF73  EF6A 9A72 F1F5 D055 EBC5
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.0 (GNU/Linux)
Comment: For info see http://www.gnupg.org

iD8DBQE7zv1TmnLx9dBV68URAisEAJ4nNYz4lxpgWojULE/Xo9SUb5IexgCfS9At
J6kAVn/3vFHeJkl9bjr4AcQ=
=W4xQ
-----END PGP SIGNATURE-----

Re: Doing a regexp-based search/replace?

From

Stephan Szabo

Date:

18 October 2001, 19:06:19

Well, the easiest general way is probably a plperl function, but I think
the following may work for your specific case:

update mytable setproperty_id=substr(property_id, 1, position('-' in property_id)-1) where position('-' in
property_id)!=0;


On Thu, 18 Oct 2001, Steve Frampton wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Hello:
> 
> I've got a table containing property_id's with values of the form
> ###-####.  I would like to discard the slash onwards (and I can't use a
> substr() because I am not guaranteed if a) the -#### portion exists, b)
> what position it exists from.
> 
> If this were a text file, I would use a sed expression such as:
> 
> cat textfile | sed 's/-.*$//'
> 
> I've been looking for a way to do this with PostgreSQL but so far haven't
> found a function that seems to be suitable.  I thought maybe I could do it
> with translate, but translate doesn't appear to work with regular
> expressions.  So far I've tried things like:
> 
> select translate(property_id, '-.*', '') from mytable;
> 
> I need to do this, because the -.* portion of my property_id was entered
> in error, and I would like to do an update on the entire table and just
> have the left-hand side of the property_id column remaining.

Re: Doing a regexp-based search/replace?

From

Brett Schwarz

Date:

18 October 2001, 19:27:16

You could write a Tcl (i.e. pltcl) function, and use that to do what you want:

CREATE FUNCTION remove(varchar) RETURNS varchar AS '
set input $1
regsub -- {-.*$} $input {} output
return $output

' language 'pltcl';


[NOTE: untested]

you may have to monkey with the regexp to get exactly what you want...


--brett



On Thu, 18 Oct 2001 12:03:28 -0400 (EDT)
Steve Frampton <frampton@LinuxNinja.com> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Hello:
> 
> I've got a table containing property_id's with values of the form
> ###-####.  I would like to discard the slash onwards (and I can't use a
> substr() because I am not guaranteed if a) the -#### portion exists, b)
> what position it exists from.
> 
> If this were a text file, I would use a sed expression such as:
> 
> cat textfile | sed 's/-.*$//'
> 
> I've been looking for a way to do this with PostgreSQL but so far haven't
> found a function that seems to be suitable.  I thought maybe I could do it
> with translate, but translate doesn't appear to work with regular
> expressions.  So far I've tried things like:
> 
> select translate(property_id, '-.*', '') from mytable;
> 
> I need to do this, because the -.* portion of my property_id was entered
> in error, and I would like to do an update on the entire table and just
> have the left-hand side of the property_id column remaining.
> 
> Any ideas?  Thank you in advance.
> 
> - ---------------< LINUX: The choice of a GNU generation. >-------------
> Steve Frampton   <frampton@LinuxNinja.com>   http://www.LinuxNinja.com
> GNU Privacy Guard ID: D055EBC5  (see http://www.gnupg.org for details)
> GNU-PG Fingerprint: EEFB F03D 29B6 07E8 AF73  EF6A 9A72 F1F5 D055 EBC5
> -----BEGIN PGP SIGNATURE-----
> Version: GnuPG v1.0.0 (GNU/Linux)
> Comment: For info see http://www.gnupg.org
> 
> iD8DBQE7zv1TmnLx9dBV68URAisEAJ4nNYz4lxpgWojULE/Xo9SUb5IexgCfS9At
> J6kAVn/3vFHeJkl9bjr4AcQ=
> =W4xQ
> -----END PGP SIGNATURE-----
> 
> 
> ---------------------------(end of broadcast)---------------------------
> TIP 4: Don't 'kill -9' the postmaster

_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com

Re: Doing a regexp-based search/replace?

From

Tom Lane

Date:

18 October 2001, 20:13:43

Steve Frampton <frampton@LinuxNinja.com> writes:
> If this were a text file, I would use a sed expression such as:
> cat textfile | sed 's/-.*$//'
> I've been looking for a way to do this with PostgreSQL but so far haven't
> found a function that seems to be suitable.

Write a function in pltcl or plperl, either of which can mash text
strings with ease and abandon ...
        regards, tom lane

Re: Doing a regexp-based search/replace?

From

"Josh Berkus"

Date:

18 October 2001, 22:36:10

Steve,

> I've got a table containing property_id's with values of the form
> ###-####.  I would like to discard the slash onwards (and I can't use
> a
> substr() because I am not guaranteed if a) the -#### portion exists,
> b)
> what position it exists from.
> 
> If this were a text file, I would use a sed expression such as:
> 
> cat textfile | sed 's/-.*$//'

In SQL/plpgsql, you can't do this with a single expression.  However,
you can do it with three expressions put together.

CREATE FUNCTION remove_propid_tail (VARCHAR ) RETURNS VARCHAR AS'
SELECT SUBSTR($1, 1, ((STRPOS($1, ''-'') - 1));
END;'
LANGUAGE 'SQL';

Then run:

UPDATE main_table SET property_id = remove_propid_tail(property_id)
WHERE property_id ~ '-';

-Josh

______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

Re: Deleting obsolete values

From

"Pat M"

Date:

23 October 2001, 14:49:37

Delete from partitur where userid NOT IN (SELECT DISTINCT ON (userid)
userid, val, ts FROM partitur)

"Haller Christoph" <ch@rodos.fzk.de> wrote in message
news:200110161445.QAA11833@rodos...
> This may look familiar to you - it was on the list last month.
> Consider the following table
> create table partitur
>  (userid text, val integer, ts timestamp DEFAULT NOW() );
> Do some inserts
> insert into partitur values('Bart', 1440);
> insert into partitur values('Lisa', 1024);
> insert into partitur values('Bart', 7616);
> insert into partitur values('Lisa', 3760);
> insert into partitur values('Bart', 3760);
> insert into partitur values('Lisa', 7616);
> To retrieve the latest values (meaning the last ones inserted)
> Tom Lane wrote
> >This is what SELECT DISTINCT ON was invented for.  I don't know any
> >comparably easy way to do it in standard SQL, but with DISTINCT ON
> >it's not hard:
> >SELECT DISTINCT ON (userid) userid, val, ts FROM partitur
> >ORDER BY userid, ts DESC;
>
> My question now is
> Is there a way to delete all rows the select statement did not
> bring up?
> After that *unknown* delete statement
> select userid, val, ts from partitur ;
> should show exactly the same as the SELECT DISTINCT ON (userid) ...
> did before.
>
> Regards, Christoph
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: you can get off all lists at once with the unregister command
>     (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)