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(at)postgresql(dot)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 sequence and 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 anticipate p_number_of_items being more than 20.

--
Peter Headland
Architect
Actuate Corporation

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

2009/8/11 D'Arcy J.M. Cain <darcy(at)druid(dot)net>:
> On Mon, 10 Aug 2009 17:52:36 -0700
> "Peter Headland" <pheadland(at)actuate(dot)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

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