Re: [planner] Ignore "order by" in subselect if parrent do count(*)

Поиск
Список
Период
Сортировка
От Tom Lane
Тема Re: [planner] Ignore "order by" in subselect if parrent do count(*)
Дата
Msg-id 17997.1330637364@sss.pgh.pa.us
обсуждение исходный текст
Ответ на Re: [planner] Ignore "order by" in subselect if parrent do count(*)  (Craig James <cjames@emolecules.com>)
Список pgsql-performance
Craig James <cjames@emolecules.com> writes:
> On Thu, Mar 1, 2012 at 9:50 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Considering that ORDER BY in a subquery isn't even legal per spec,

> That's surprising ... normally it won't affect the result, but with an
> offset or limit it would.  Does the offset or limit change the "not
> even legal" part?

Well, actually, the SQL standard didn't have anything comparable to
offset/limit until SQL:2008, either.  But I have to take back my
statement above.  It wasn't legal in SQL99, but evidently they added it
in the 2003 or 2008 edition, presumably to go with the limit
functionality.

Anyway, the long and the short of it is that people depend on ORDER BY
in subqueries to be honored, and we're not going to break that.

            regards, tom lane

В списке pgsql-performance по дате отправления:

Предыдущее
От: Tom Lane
Дата:
Сообщение: Re: Bad estimation for "where field not in"
Следующее
От: Stefan Keller
Дата:
Сообщение: Re: PG as in-memory db? How to warm up and re-populate buffers? How to read in all tuples into memory?