Re: Updating a specific number of rows in pl/pgsql

> Unfortunately, there is no single column that provides a unique id.

Correction - I did not understand what ctid was, but now I do, so I will try your tip.

-- 
Peter Headland
Architect
Actuate Corporation


-----Original Message-----
From: Peter Headland 
Sent: Tuesday, August 11, 2009 10:05
To: 'Pavel Stehule'; D'Arcy J.M. Cain
Cc: pgsql-sql@postgresql.org
Subject: RE: [SQL] Updating a specific number of rows in pl/pgsql

> there are one fast trick
> http://www.postgres.cz/index.php/PostgreSQL_SQL_Tricks#Fast_first_n_rows_removing

Thanks - that's a very useful page!

Unfortunately, there is no single column that provides a unique id, and I am reluctant to add one (for example, using a
sequenceand a new index) for performance reasons.
 

Given that additional constraint, is my original plan using a loop to iterate over a cursor reasonable? I don't
anticipatep_number_of_items being more than 20.
 

-- 
Peter Headland
Architect
Actuate Corporation


-----Original Message-----
From: Pavel Stehule [mailto:pavel.stehule@gmail.com] 
Sent: Tuesday, August 11, 2009 03:55
To: D'Arcy J.M. Cain
Cc: Peter Headland; pgsql-sql@postgresql.org
Subject: Re: [SQL] Updating a specific number of rows in pl/pgsql

2009/8/11 D'Arcy J.M. Cain <darcy@druid.net>:
> On Mon, 10 Aug 2009 17:52:36 -0700
> "Peter Headland" <pheadland@actuate.com> wrote:
>> I can get the rows I want to update like this:
>>
>>   SELECT *
>>    FROM queue
>>    WHERE id = p_queue_id
>>    ORDER BY rank
>>    LIMIT p_number_of_items;
>>
>> Of course, there may not be p_number_of_items available in the queue.
>>
>> I want to update all the rows in the cursor in the same way:
>>
>>   UPDATE queue SET assigned = TRUE;
>
> Assuming that there is a unique identifier on queue, let's call it
> queue_id, you should be able to do something like this:
>
>  UPDATE queue SET assigned = TRUE
>  WHERE queue_id IN (SELECT queue_id
>    FROM queue
>    WHERE id = p_queue_id
>    ORDER BY rank
>    LIMIT p_number_of_items);
>

there are one fast trick
http://www.postgres.cz/index.php/PostgreSQL_SQL_Tricks#Fast_first_n_rows_removing

p.s. replace DELETE by UPDATE
regards
Pavel Stehule

> --
> D'Arcy J.M. Cain <darcy@druid.net>         |  Democracy is three wolves
> http://www.druid.net/darcy/                |  and a sheep voting on
> +1 416 425 1212     (DoD#0082)    (eNTP)   |  what's for dinner.
>
> --
> Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
> To make changes to your subscription:
> http://www.postgresql.org/mailpref/pgsql-sql
>