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

From: Bruce Momjian <maillist(at)candle(dot)pha(dot)pa(dot)us>
To: vadim(at)sable(dot)krasnoyarsk(dot)su (Vadim B(dot) Mikheev)
Cc: herouth(at)oumail(dot)openu(dot)ac(dot)il, hackers(at)postgreSQL(dot)org (PostgreSQL-development)
Subject: Re: [QUESTIONS] How fully will subselects be implemented?
Date: 1998-02-25 14:28:10
Message-ID: 199802251428.JAA01718@candle.pha.pa.us
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>
> 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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