Re: [QUESTIONS] How fully will subselects be implemented?

Bruce Momjian <maillist@candle.pha.pa.us>

From: Bruce Momjian <maillist@candle.pha.pa.us>
To: vadim@sable.krasnoyarsk.su (Vadim B. Mikheev)
Cc: herouth@oumail.openu.ac.il, hackers@postgreSQL.org (PostgreSQL-development)
Date: 1998-02-25T14:28:10Z
Lists: pgsql-hackers
> 
> First, this list is not right place to ask about 6.3 features :)
> 2nd, subselects within UPDATE are supported.

They are?  I thought he wanted to do:

	update test set x = (select y from taby)

I didn't think we supported that.  Can you confirm that?
 
> 3rd, there will be separate select (better say - separate re-scan of
> subquery' plan) for each parent row (I assume that you talk about 
> correlated subqueries) but this will be more efficient than using 
> SQL-funcs which do _initialization_, scannig, _closing_ of query' plan
> for each parent row. When using subqueries performance will be
> near the same as for performing Nestloop join.

Good.

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