Re: SQL feature requests
От | Chuck McDevitt |
---|---|
Тема | Re: SQL feature requests |
Дата | |
Msg-id | EB48EBF3B239E948AC1E3F3780CF8F880277B2AC@MI8NYCMAIL02.Mi8.com обсуждение исходный текст |
Ответ на | Re: SQL feature requests ("Florian G. Pflug" <fgp@phlo.org>) |
Ответы |
Re: SQL feature requests
(Tom Lane <tgl@sss.pgh.pa.us>)
|
Список | pgsql-hackers |
> -----Original Message----- > From: pgsql-hackers-owner@postgresql.org [mailto:pgsql-hackers- > owner@postgresql.org] On Behalf Of Florian G. Pflug > Sent: Thursday, August 23, 2007 11:04 AM > To: Ben Tilly > Cc: Michael Glaesemann; Gregory Stark; pgsql-hackers@postgresql.org > Subject: Re: [HACKERS] SQL feature requests > > Ben Tilly wrote: > > On 8/22/07, Michael Glaesemann <grzm@seespotcode.net> wrote: > >> On Aug 22, 2007, at 20:49 , Ben Tilly wrote: > >> > >>> If your implementation accepts: > >>> > >>> group by case when true then 'foo' end > >> What would that mean? Regardless of whether or not it's accepted, it > >> should have *some* meaning. > > > > To my eyes it has a very clear meaning, we're grouping on an > > expression that happens to be a constant. Which happens to be the > > same for all rows. Which is a spectacularly useless thing to > actually > > do, but the ability to do it happens to be convenient when I'm > looking > > for something to terminate a series of commas in a dynamically built > > query. > > Which is the same very clear meaning that "group by 1" has - we're > grouping on a expression which happens to be the constant 1. Hey, > wait a second. This isn't what "group by 1" means at all - it > rather means group by whatever the fist column in the select list is. > > So, yes, "group by 'foo'" *seems* to have a very clear meaning - but > that clearness vanishes as soon as you take into account what "group by > 1" > means. > > greetings, Florian Pflug > Except "group by 1" meaning "group by column 1" is a PostgreSQL extension, not a SQL standard feature, if I recall. Anyway, I suppose this should work like ORDER BY... For some reason, we allow all expressions in ORDER BY *except* the degeneratecase of a constant (ugly). Expressions in ORDER BY are a PostgreSQL extension also... Not sure why we disallow the case of a constant, except somebodywas worried that it would confuse users, because simple integer constants are treated special. But it seems strange that this is legal in PostgreSQL: Select * from x order by trim('foo'); But this is illegal: Select * from x order by 'foo'; And this is accepted, but orders on the constant "1" rather than on column 1: select * from x order by 1::int;
В списке pgsql-hackers по дате отправления: