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From: Chris Browne <cbbrowne@acm.org>
X-Newsgroups: pgsql.sql
Subject: Re: Is this a bug? Deleting a column deletes the constraint.
Date: Thu, 12 Oct 2006 10:56:14 -0400
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dev@freedomcircle.net (Joe) writes:
> On Thu, 2006-10-12 at 01:25 -0400, Tom Lane wrote:
>> It does seem like this is wrong, in view of SQL92's statement about
>> ALTER TABLE DROP COLUMN:
>> 
>>          4) If RESTRICT is specified, then C shall not be referenced in
>>             the <query expression> of any view descriptor or in the <search
>>             condition> of any constraint descriptor other than a table con-
>>             straint descriptor that contains references to no other column
>>             and that is included in the table descriptor of T.
>> 
>> IOW we should only allow unique constraints to be auto-dropped if
>> they reference just the one single column.  Ick.
>
> I didn't realize before that you can also drop all columns, leaving a
> table without *any* columns.  Is that a SQL92 "feature"?

You can create a table without any columns.

tutorial=# create table empty_table ();
CREATE TABLE
tutorial=# \d empty_table 
Table "public.empty_table"
 Column | Type | Modifiers 
--------+------+-----------

tutorial=# select * from empty_table ;
  
--
(0 rows)

A table without columns is of pretty limited usefulness, until you add
some columns, but having a form of "zero" seems not insensible...
-- 
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