Re: null foreign key column

Vernon Wu wrote:

>12/02/2003 2:24:49 PM, Dmitry Tkach  wrote:
>
>  
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>>You don't want it to be serial - just make it 'person_id in'
>>    
>>
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>Any reasons?
>  
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Yeah... Two of them:

- It does not make sense for a serial column to reference other tables - 
the only purpose of serial is to generate unique keys, in your case you 
do not want them generated, but rather copied from the entries in the 
referenced table.

- The other reason is that 'serial' implies 'not null' - that is why 
your insert statement fails.

Dima

>  
>
>>I hope, it helps...
>>
>>Dima
>>
>>Arunachalam Jaisankar wrote:
>>    
>>
>>>This is a multi-part message in MIME format.
>>>
>>>------=_NextPart_000_0005_01C2D1EE.61998D70
>>>Content-Type: text/plain;
>>>	charset="iso-8859-1"
>>>Content-Transfer-Encoding: quoted-printable
>>>
>>>Hi all,
>>>
>>>I would like to have a foreign key column in my table which allows null val=
>>>ue also.
>>>But the below create table sql command doesn't accept null value for person=
>>>_id.
>>>How to do in postgres?
>>>
>>>create table event
>>>(
>>>    event_id               serial                not null,
>>>    event_description      char(255)                     ,
>>>    person_id              serial                        ,
>>>    primary key (event_id),
>>>    foreign key  (person_id)
>>>       references person (person_id)
>>>);
>>>
>>>regards
>>>Jai
>>>------=_NextPart_000_0005_01C2D1EE.61998D70
>>>Content-Type: text/html;
>>>	charset="iso-8859-1"
>>>Content-Transfer-Encoding: quoted-printable
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
Hi all,
>>>
 
>>>
I would like to have a foreign key column =
>>>in my=20
>>>table which allows null value also.
>>>
But the below create table sql command doe=
>>>sn't=20
>>>accept null value for person_id.
>>>
How to do in postgres?
>>>
=
>>> 
>>>
create table event
(
  &nb=
>>>sp;=20
>>>event_id           &=
>>>nbsp;  =20
>>>serial           &nb=
>>>sp;   =20
>>>not null,
    event_description    &n=
>>>bsp;=20
>>>char(255)           =
>>>         =20
>>>,
   =20
>>>person_id           =
>>>  =20
>>>serial           &nb=
>>>sp;           =20
>>>,
    primary key (event_id),
    forei=
>>>gn=20
>>>key  (person_id)
       references pe=
>>>rson=20
>>>(person_id)
);
>>>
 
>>>
regards
>>>
Jai
>>>
>>>------=_NextPart_000_0005_01C2D1EE.61998D70--
>>>
>>>      
>>>
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>>    
>>
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