Marco Colombo wrote:
That is, given a variable A, you can always write a boolean expression
that evaluates True or False to test if A is _equal_ to None/undef/NULL
(in C):
And of course you can do this in SQL as well.
('a', NULL) is neither the same _nor different_ from ('a', 2).
Uh, I'm not sure w
On Thu, Apr 28, 2005 at 02:04:29PM +0200,
Marco Colombo <[EMAIL PROTECTED]> wrote
a message of 146 lines which said:
> No. NULL is NOT 'None', nor 'undef', and definitely not NULL as in
> C.
Thanks for the very good and detailed explanation of NULL in
SQL. Curious people may note that the stra
On Wed, 2005-04-27 at 17:00 +0200, Stephane Bortzmeyer wrote:
> On Wed, Apr 27, 2005 at 09:36:57AM -0500,
> Scott Marlowe <[EMAIL PROTECTED]> wrote
> a message of 18 lines which said:
>
> > Often the best bet here, btw, is to declare it not null then use
> > something other than null to represe
On Wed, Apr 27, 2005 at 05:04:07PM +0200,
Sebastian Böck <[EMAIL PROTECTED]> wrote
a message of 24 lines which said:
One is enough :-)
v
> CREATE TABLE table x (
> name TEXT NOT NULL,
> address INET
> );
>
> CREATE UNIQUE INDEX na ON x (name, address);
> C
On Wed, Apr 27, 2005 at 09:36:57AM -0500,
Scott Marlowe <[EMAIL PROTECTED]> wrote
a message of 18 lines which said:
> Often the best bet here, btw, is to declare it not null then use
> something other than null to represent null, like the text
> characters NA or something.
Yes, but it defeats
On Wed, Apr 27, 2005 at 04:50:23PM +0200,
Sebastian Böck <[EMAIL PROTECTED]> wrote
a message of 48 lines which said:
> CREATE UNIQUE INDEX na ON x (name, address) WHERE address IS NULL;
No, because it prevents two tuples with the same value of "name".
---(end of broadc
Stephane Bortzmeyer <[EMAIL PROTECTED]> writes:
> Yes, PostgreSQL is right and implement the standard. Now, what's the
> rationale for the standard? I understand it for a single column but,
> for several columns, it should be still possible to have different
> tuples, such as (3, NULL) and (5, NULL
On Wed, Apr 27, 2005 at 10:26:30AM -0400,
Tom Lane <[EMAIL PROTECTED]> wrote
a message of 9 lines which said:
> If that's what you want, declare it as UNIQUE not PRIMARY KEY.
As shown by Patrick TJ McPhee, it does not work:
tests=> create table x (
tests(>name TEXT NOT NULL,
tests(>a
On Wed, Apr 27, 2005 at 05:19:32AM +,
Patrick TJ McPhee <[EMAIL PROTECTED]> wrote
a message of 37 lines which said:
> but you should know that in SQL, unique constraints don't apply to
> rows containing null values
May be I should but I didn't.
> your table definition will be as you want
On Wed, 2005-04-27 at 02:12, Stephane Bortzmeyer wrote:
> On Tue, Apr 26, 2005 at 03:48:44PM -0500,
> Scott Marlowe <[EMAIL PROTECTED]> wrote
> a message of 26 lines which said:
>
> > Here's a quote from the SQL1992 spec that's VERY clear:
>
> Yes, PostgreSQL is right and implement the standar
In article <[EMAIL PROTECTED]>,
Stephane Bortzmeyer <[EMAIL PROTECTED]> wrote:
% But it does not apply to primary keys containing a group of
% columns. In that case (my case), columns do not have to be UNIQUE. But
% they have to be NOT NULL, which puzzles me.
It does apply to primary keys contain
On Tue, Apr 26, 2005 at 03:48:44PM -0500,
Scott Marlowe <[EMAIL PROTECTED]> wrote
a message of 26 lines which said:
> Here's a quote from the SQL1992 spec that's VERY clear:
Yes, PostgreSQL is right and implement the standard. Now, what's the
rationale for the standard? I understand it for a s
On Tue, Apr 26, 2005 at 03:22:40PM -0500,
Guy Rouillier <[EMAIL PROTECTED]> wrote
a message of 37 lines which said:
> "The primary key constraint specifies that a column or columns of a
> table may contain only unique (non-duplicate), nonnull values.
> Technically, PRIMARY KEY is merely a combi
Stephane Bortzmeyer wrote:
> If I define a primary key:
>
>name TEXT NOT NULL,
>address INET,
>PRIMARY KEY(name, address)
>
> the definition (seen by \d) becomes:
>
> name | text| not null
> address | inet|
If I define a primary key:
name TEXT NOT NULL,
address INET,
PRIMARY KEY(name, address)
the definition (seen by \d) becomes:
name | text| not null
address | inet| not null
"address" is now not null, which I d
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