Обсуждение: SQL question.

Hello SQL Aces !

I want to do a select on a table distinct on linkid and sorted by
date. I have try this

SELECT DISTINCT ON (linkid) * FROM all_links
   WHERE uid='2' AND DATE_TRUNC('day',read_date) = DATE_TRUNC('day',
         TIMESTAMP '2005-06-01') ORDER BY linkid, read_date;

With this request "works" but the raws are sorted as I want. To have
the rows sorted by date I have done this using a temporary table and
that works exactly as I want.

CREATE LOCAL TEMP TABLE temp_links WITHOUT OIDS AS
   SELECT DISTINCT ON (linkid) * FROM all_links
   WHERE uid='2' AND DATE_TRUNC('day',read_date) = DATE_TRUNC('day',
         TIMESTAMP '2005-06-01') ORDER BY linkid;

SELECT * from temp_links ORDER BY read_date DESC limit 100

My question is... How can I do the same thing in the more efficient
way and without using a temporary table. Since I am using PHP and the
table is not deleted at the end of the program because PHP keeps the
connection to the database open.

Thanks for any suggestions.
Fred

how about (untested)

select *
from
(
SELECT DISTINCT ON (linkid) *
FROM all_links
WHERE uid='2' AND DATE_TRUNC('day',read_date) = DATE_TRUNC('day',TIMESTAMP '2005-06-01')
ORDER BY linkid
) A
ORDER BY read_date DESC limit 100


---------- Original Message -----------
From: FC <lne-1mc8@myamail.com>
To: pgsql-general@postgresql.org
Sent: Wed, 1 Jun 2005 16:40:48 +0200
Subject: [GENERAL] SQL question.

> Hello SQL Aces !
>
> I want to do a select on a table distinct on linkid and sorted by
> date. I have try this
>
> SELECT DISTINCT ON (linkid) * FROM all_links
>    WHERE uid='2' AND DATE_TRUNC('day',read_date) = DATE_TRUNC('day',
>          TIMESTAMP '2005-06-01') ORDER BY linkid, read_date;
>
> With this request "works" but the raws are sorted as I want. To have
> the rows sorted by date I have done this using a temporary table and
> that works exactly as I want.
>
> CREATE LOCAL TEMP TABLE temp_links WITHOUT OIDS AS
>    SELECT DISTINCT ON (linkid) * FROM all_links
>    WHERE uid='2' AND DATE_TRUNC('day',read_date) = DATE_TRUNC('day',
>          TIMESTAMP '2005-06-01') ORDER BY linkid;
>
> SELECT * from temp_links ORDER BY read_date DESC limit 100
>
> My question is... How can I do the same thing in the more efficient
> way and without using a temporary table. Since I am using PHP and the
> table is not deleted at the end of the program because PHP keeps the
> connection to the database open.
>
> Thanks for any suggestions.
> Fred
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: you can get off all lists at once with the unregister command
>     (send "unregister YourEmailAddressHere" to majordomo@postgresql.org)
------- End of Original Message -------

On Wed, Jun 01, 2005 at 04:40:48PM +0200, FC wrote:
>
> Hello SQL Aces !
>
> I want to do a select on a table distinct on linkid and sorted by
> date. I have try this

How about a subquery?:

SELECT * FROM
 ( SELECT DISTINCT ON (linkid) * FROM all_links
   WHERE uid='2' AND DATE_TRUNC('day',read_date) = DATE_TRUNC('day',
         TIMESTAMP '2005-06-01') ORDER BY linkid, read_date) AS sub
ORDER BY read_date DESC limit 100;

Hope this helps,

> My question is... How can I do the same thing in the more efficient
> way and without using a temporary table. Since I am using PHP and the
> table is not deleted at the end of the program because PHP keeps the
> connection to the database open.
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a
> tool for doing 5% of the work and then sitting around waiting for someone
> else to do the other 95% so you can sue them.

I need to remember to keep things simple...

Works fine, thanks.

Fred


On Jun 1, 2005, at 5:20 PM, Jim Buttafuoco wrote:

> how about (untested)
>
> select *
> from
> (
> SELECT DISTINCT ON (linkid) *
> FROM all_links
> WHERE uid='2' AND DATE_TRUNC('day',read_date) = DATE_TRUNC
> ('day',TIMESTAMP '2005-06-01')
> ORDER BY linkid
> ) A
> ORDER BY read_date DESC limit 100
>
>
> ---------- Original Message -----------
> From: FC <lne-1mc8@myamail.com>
> To: pgsql-general@postgresql.org
> Sent: Wed, 1 Jun 2005 16:40:48 +0200
> Subject: [GENERAL] SQL question.
>
>
>> Hello SQL Aces !
>>
>> I want to do a select on a table distinct on linkid and sorted by
>> date. I have try this
>>
>> SELECT DISTINCT ON (linkid) * FROM all_links
>>    WHERE uid='2' AND DATE_TRUNC('day',read_date) = DATE_TRUNC('day',
>>          TIMESTAMP '2005-06-01') ORDER BY linkid, read_date;
>>
>> With this request "works" but the raws are sorted as I want. To have
>> the rows sorted by date I have done this using a temporary table and
>> that works exactly as I want.
>>
>> CREATE LOCAL TEMP TABLE temp_links WITHOUT OIDS AS
>>    SELECT DISTINCT ON (linkid) * FROM all_links
>>    WHERE uid='2' AND DATE_TRUNC('day',read_date) = DATE_TRUNC('day',
>>          TIMESTAMP '2005-06-01') ORDER BY linkid;
>>
>> SELECT * from temp_links ORDER BY read_date DESC limit 100
>>
>> My question is... How can I do the same thing in the more efficient
>> way and without using a temporary table. Since I am using PHP and the
>> table is not deleted at the end of the program because PHP keeps the
>> connection to the database open.
>>
>> Thanks for any suggestions.
>> Fred
>>
>> ---------------------------(end of
>> broadcast)---------------------------
>> TIP 2: you can get off all lists at once with the unregister command
>>     (send "unregister YourEmailAddressHere" to
>> majordomo@postgresql.org)
>>
> ------- End of Original Message -------
>
>
>

I have all my database encoded in ISO-8859-1 and I would like to
convert this database in UNICODE.

I have try this but with no success.

pg_dump dbase > foo.db
createdb -E UNICODE dbase
psql dbase < foo.db

I have also try to modify the value of client_encoding in the foo.db
file but that didn't fix my problem.

Thanks.
Fred