Joseph Shraibman <[EMAIL PROTECTED]> writes:
> From the postgres docs:
> A sub-SELECT can appear in the FROM clause. This acts as though its output
>were
> created as a temporary table for the duration of this single SELECT command. Note
>that the
> sub-SELECT must be surrounded by parentheses, and an alias must be provided for it.
> So does postgres actually use a temporary table behind the scenses?
No.
The point of that part of the docs is that the sub-SELECT's result is
(logically) computed independently of the query that it appears in ---
thus, you can't have references to tables that aren't part of that
sub-SELECT. This is a lot different from subselects in WHERE, the
select target list, etc, since they can depend on their context.
If you can think of a clearer way of phrasing the docs, let's have it.
regards, tom lane
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