Re: Derived tables?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: CSN <cool_screen_name90001(at)yahoo(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Derived tables?
Date: 2004-10-28 22:39:39
Message-ID: 7905.1099003179@sss.pgh.pa.us
Views: Raw Message | Whole Thread | Download mbox | Resend email
Thread:
Lists: pgsql-general

CSN <cool_screen_name90001(at)yahoo(dot)com> writes:
> Just wondering - does PG support derived tables? I'm
> not really sure what the difference is between them
> and subqueries.

None whatever, at least using the definition offered by your second
reference:

A derived table is a select statement inside parenthesis, with
an alias, used as a table in a join.

The SQL92 spec appears to use the phrase in exactly this way (except
they don't require the construct to appear in a join, as indeed we don't
either; the most correct explanation would probably be "used as a table
in a FROM clause").

MySQL often has their own spin on such terms ;-). I'm not sure what
MySQL 4.1 actually supports in this line. But I'll make a side bet that
they don't yet optimize them as well as we do ...

regards, tom lane

In response to

Browse pgsql-general by date

  From Date Subject
Next Message Jim C. Nasby 2004-10-28 22:47:10 Re: Reasoning behind process instead of thread based
Previous Message Jim C. Nasby 2004-10-28 22:37:29 Turning a subselect into an array