Message-ID: <3E520C32.CD9C82FA@rodos.fzk.de>
Date: Tue, 18 Feb 2003 11:34:26 +0100
From: Christoph Haller <ch@rodos.fzk.de>
MIME-Version: 1.0
To: pgsql-sql@postgresql.org
Cc: mallah@trade-india.com
Subject: Re: " Adding missing FROM-clause entry for table .... " problem.
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>
> We find that if we alias a tablename and refer to that tablename in
where cluase instead of reffering
> to the alias it produces wrond results.
>
> EG:
> select to_char(a.generated, 'DD/Mon/YYYY' ) ,userid,email,descr from
membership_invoice a join payment_classes using(
payment_class)
> join users using(userid)  join membership_status using(userid) where
membership_invoice.status='a' and granted is fa
lse and
> membership_invoice.last_reminder is null and current_date -
date(a.generated) > 4  limit 10 ;
> NOTICE:  Adding missing FROM-clause entry for table
"membership_invoice"
>
> Where as merely rewriting the quer to use defined aliases gives the
correct results.
>
> select to_char(a.generated, 'DD/Mon/YYYY' ) ,userid,email,descr from
membership_invoice a join payment_classes
> using(payment_class) join users using(userid)  join membership_status
using(userid) where  a.status='a' and granted i
s
> false and a.last_reminder is null and current_date - date(a.generated)
> 4   ;
>
> Can Anyone please explain if its a BUG or problem in my understanding
>
I think it's a problem in understanding. The documentation (7.2.1)
states (as the NOTICE: does)

2.2.1.3. Table and Column Aliases

A temporary name can be given to tables and complex table references to
be used for references to the derived table in further
processing. This is called a table alias.

FROM table_reference AS alias

Here, alias can be any regular identifier. The alias becomes the new
name of the table reference for the current query -- it is no
longer possible to refer to the table by the original name. Thus

SELECT * FROM my_table AS m WHERE my_table.a > 5;

is not valid SQL syntax. What will actually happen (this is a PostgreSQL
extension to the standard) is that an implicit table
reference is added to the FROM clause, so the query is processed as if
it were written as

SELECT * FROM my_table AS m, my_table AS my_table WHERE my_table.a > 5;

Regards, Christoph