| From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com>, Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> |
| Cc: | Surafel Temsgen <surafel3000(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: FETCH FIRST clause WITH TIES option |
| Date: | 2018-11-01 10:38:46 |
| Message-ID: | 65ecc991-97aa-50a2-7131-10c8b3991c8c@2ndquadrant.com |
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| Lists: | pgsql-hackers |
On 10/31/2018 06:17 PM, Robert Haas wrote:
> On Mon, Oct 29, 2018 at 12:48 PM Andrew Gierth
> <andrew(at)tao11(dot)riddles(dot)org(dot)uk> wrote:
>> Then FETCH FIRST N WITH TIES becomes "stop when the expression
>> rank() over (order by ...) <= N
>> is no longer true" (where the ... is the existing top level order by)
>
> Wouldn't that be wicked expensive compared to something hard-coded
> that does the same thing?
>
Not sure, but that was one of my concerns too, particularly for the
simple FETCH FIRST N WITH TIES case. But I think Andrew has a point it
would make it much easier to implement the PERCENT case.
regards
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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