Derived tables?

[CSN]

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...e_2004_32.html
http://www.sqlservercentral.com/colu...intversion.asp

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[Tom Lane]

CSN <co*******************@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

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