Re: Nested query performance issue

От: Tom Lane
Тема: Re: Nested query performance issue
Дата: ,
Msg-id: 21534.1239370946@sss.pgh.pa.us
(см: обсуждение, исходный текст)
Ответ на: Re: Nested query performance issue  (Glenn Maynard)
Список: pgsql-performance

Скрыть дерево обсуждения

Nested query performance issue  (Glenn Maynard, )
 Re: Nested query performance issue  (Віталій Тимчишин, )
  Re: Nested query performance issue  (Glenn Maynard, )
   Re: Nested query performance issue  (Віталій Тимчишин, )
    Re: Nested query performance issue  (Glenn Maynard, )
    Re: Nested query performance issue  (Greg Smith, )
    Re: Nested query performance issue  (Merlin Moncure, )
 Re: Nested query performance issue  (Heikki Linnakangas, )
  Re: Nested query performance issue  (Glenn Maynard, )
   Re: Nested query performance issue  (Matthew Wakeling, )
    Re: Nested query performance issue  (Glenn Maynard, )
  Re: Nested query performance issue  (Glenn Maynard, )
   Re: Nested query performance issue  (Tom Lane, )

Glenn Maynard <> writes:
> http://www.postgresql.org/docs/8.3/static/xfunc-sql.html says this is
> deprecated (though no deprecation warning is being generated):

>> Currently, functions returning sets can also be called in the select list of a query. For each row that the query
generatesby itself, the function returning set is invoked, and an output row is generated for each element of the
function'sresult set. Note, however, that this capability is deprecated and might be removed in future releases. 

The way to parse that is "we don't like this and we will get rid of it
if we can ever figure out a good substitute".  Right now there is no
100% substitute, so it stays.  (In fact, 8.4 will extend the feature so
it works in cases that don't work today, like for PL functions.)

There are, however, good reasons not to like it, such as the rather
questionable behavior if there's more than one SRF in the same select
list.  Don't complain if you run into that wart.

            regards, tom lane


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