From: | Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com> |
---|---|
To: | Neil Zanella <nzanella(at)cs(dot)mun(dot)ca> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: AS operator and subselect result names: PostgreSQL |
Date: | 2003-11-02 22:16:34 |
Message-ID: | 20031102141232.P85650@megazone.bigpanda.com |
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Thread: | |
Lists: | pgsql-general |
On Fri, 31 Oct 2003, Neil Zanella wrote:
> Hello,
>
> I would like to ask the about the following...
>
> PostgreSQL allows tables resulting from subselects to be renamed with
> an optional AS keyword whereas Oracle 9 will report an error whenever
> a table is renamed with the AS keyword. Furthermore, in PostgreSQL
> when the result of a subselect is referenced in an outer select
> it is required that the subselect result be named, whereas this
> is not true in Oracle. I wonder what standard SQL has to say
> about these two issues. In particular:
>
> 1. Does standard SQL allow an optional AS keyword for (re/)naming
> tables including those resulting from subselects.
>
> and
>
> 2 Why must a subselect whose fields are referenced in an outer query
> be explicitly named in PostgreSQL when it is not necessary in Oracle.
I believe the section in question of SQL92 that you're asking about
says explicitly that a table reference from a derived table should look
like:
<derived table> [ AS ] <correlation name> [ <left paren> <derived column
list> <right paren> ]
where <derived table> is a table subquery.
It's possible that SQL99 changes this, but in SQL92 at least, it looks
like the correlation name is not optional (although the AS keyword is).
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