From: Peter Headland <pheadland@actuate.com>
To: Pavel Stehule <pavel.stehule@gmail.com>
To: D'Arcy J.M. Cain <darcy@druid.net>
Cc: pgsql-sql@postgresql.org
Subject: Re: Updating a specific number of rows in pl/pgsql
Date: Tue, 11 Aug 2009 10:05:28 -0700
Message-ID: <71F491F5DA99604A80DE49424BF3D02B0C7292EF@exchange8.actuate.com> (raw)
In-Reply-To: <162867790908110355g3b62cc56u1c74092dd01bbd8e@mail.gmail.com>
References: <71F491F5DA99604A80DE49424BF3D02B0C7290CA@exchange8.actuate.com>
<20090811062503.86993bf6.darcy@druid.net>
<162867790908110355g3b62cc56u1c74092dd01bbd8e@mail.gmail.com>
> 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.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.
>
> --
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To: pgsql-sql@postgresql.org
Cc: pheadland@actuate.com, pavel.stehule@gmail.com, darcy@druid.net
Subject: Re: Updating a specific number of rows in pl/pgsql
In-Reply-To: <71F491F5DA99604A80DE49424BF3D02B0C7292EF@exchange8.actuate.com>
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