Re: request for sql3 compliance for the update command - Mailing list pgsql-hackers

Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I wasn't sure it made logical sense to allow correlated subqueries in
> FROM because the FROM is processed before the WHERE.

It doesn't; in fact it violates the whole semantic model of SQL,
as far as I can see.  Sub-selects in FROM are (in principle)
evaluated separately and then joined.  They can't have cross-references.

I think there is some weird construct in SQL99 that alters this behavior,
though.
        regards, tom lane