Thread: Derived tables?

Just wondering - does PG support derived tables? I'm
not really sure what the difference is between them
and subqueries.

http://www.mysql.com/news-and-events/press-release/release_2004_32.html
http://www.sqlservercentral.com/columnists/rmarda/derivedtablebasics_printversion.asp



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CSN <cool_screen_name90001@yahoo.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