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Re: [SQL] select ... from (select .. from where.. ) where ... ?

From: Clark Evans <clark(dot)evans(at)manhattanproject(dot)com>
To: MESZAROS Attila <tilla(at)chiara(dot)csoma(dot)elte(dot)hu>
Cc: pgsql-sql(at)hub(dot)org
Subject: Re: [SQL] select ... from (select .. from where.. ) where ... ?
Date: 1999-03-31 20:00:45
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-sql
MESZAROS Attila wrote:
> I'am faced with a huge system using the above kind of queries.
> It was originally written and tested with adabas.

I wrote a hudge system using those kind of queries.  Very
useful buggers, really helps you manage complexity.  I bet
it plays hudge games with the optimizer though...
> Unfortunatelly 6.4 does support subqueries only in the 'where' expression,
> as far as I undersood...

That's my understanding.  6.5 will not support it either.

> My questions are:
>         How can I port this program with the least effort?
>         Shall I create views corresponding to the subqueries,
>         and doing the outer select on a view?

You can do this, as long as the inner select does not
have an aggregate.  If it has an aggregate _or_ uses an
outer join then you need to code up functions that
do the outer-join.

>         Is is planned to implement this feature in the near future?

I hope so.  Actually, I think this is a generalization of the HAVING 
clause.  About 2 years ago (using Oracle) I dropped using the HAVING
clause due to this form... so, there is another possibility,
see if you can re-write these queries to use HAVING.

Let me know if I can help more.


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Subject: Retrieving the record not matched with a join.
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