Re: avoid select expens_expr(col) like unneccessary calculations

Поиск
Список
Период
Сортировка
От Bruce Momjian
Тема Re: avoid select expens_expr(col) like unneccessary calculations
Дата
Msg-id 200307211523.h6LFNa112572@candle.pha.pa.us
обсуждение исходный текст
Ответ на Re: avoid select expens_expr(col) like unneccessary calculations  (Stephan Szabo <sszabo@megazone23.bigpanda.com>)
Список pgsql-sql
Stephan Szabo wrote:
> On 8 Jul 2003, Markus Bertheau wrote:
> 
> > when you have
> > select expensive_expression(column), * from table offset 20 limit 40
> >
> > can you somehow save the cost for the first 20 calculations of
> > expensive_expression?
> 
> Right now the only way I can think of that might work is to push the
> offset/limit into a subselect on table and then do the
> expensive_expression at the top level.

Well, you can do:
SELECT * FROM (SELECT * FROM pg_class) AS pg_class

so you could do:
SELECT func(relname), * FROM (SELECT * FROM pg_class OFFSET 20 LIMIT 40) AS pg_class

--  Bruce Momjian                        |  http://candle.pha.pa.us pgman@candle.pha.pa.us               |  (610)
359-1001+  If your life is a hard drive,     |  13 Roberts Road +  Christ can be your backup.        |  Newtown Square,
Pennsylvania19073
 


В списке pgsql-sql по дате отправления:

Предыдущее
От: "vijaykumar M"
Дата:
Сообщение: Postgresql Temporary table scripts..
Следующее
От: Jean-Luc Lachance
Дата:
Сообщение: Re: min() and NaN