Re: aggregate functions, COUNT

Поиск
Список
Период
Сортировка
От Stephan Szabo
Тема Re: aggregate functions, COUNT
Дата
Msg-id Pine.BSF.4.21.0110020944100.46517-100000@megazone23.bigpanda.com
обсуждение исходный текст
Ответ на aggregate functions, COUNT  (Kevin Way <kevin.way@overtone.org>)
Ответы Re: aggregate functions, COUNT  (Tom Lane <tgl@sss.pgh.pa.us>)
Список pgsql-sql
On Tue, 2 Oct 2001, Kevin Way wrote:

> I'm currently using a SELECT count(*) when all I really want to know is
> if 1 or more records exist.  Is there a standard way to just find out if
> a record exists?  If not, is there a way to avoid iterating over all the
> records by writing an aggregate function?  Given what I've read of how
> they work, I don't see how to make the function return before parsing
> all the results anyway, am I wrong here?

I think you could use EXISTS for that,
select EXISTS (<query>); should give a true/false on whether the 
query returned any rows.  I'm not sure if it stops after one row
or not, but if it doesn't you can add a limit 1 to the query.





В списке pgsql-sql по дате отправления:

Предыдущее
От: "Josh Berkus"
Дата:
Сообщение: Indexing behavior
Следующее
От: Devrim GUNDUZ
Дата:
Сообщение: Re: Stupid Question