Re: [SQL] null foreign key column

Dmitry Tkach Wed, 12 Feb 2003 14:40:18 -0800

Vernon Wu wrote:

12/02/2003 2:24:49 PM, Dmitry Tkach <[EMAIL PROTECTED]> wrote:

You don't want it to be serial - just make it 'person_id in'

Any reasons?

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.

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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
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charset="iso-8859-1"
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; charset=3Diso-8859-1">
<META content=3D"MSHTML 6.00.2800.1106" name=3DGENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DArial size=3D2>Hi all,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>I would like to have a foreign key column =
in my=20
table which allows null value also.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>But the below create table sql command doe=
sn't=20
accept null value for person_id.</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>How to do in postgres?</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT><FONT face=3DArial size=3D2></FONT>=
 </DIV>
<DIV><FONT face=3DArial size=3D2>create table event<BR>(<BR>  &nb=
sp;=20
event_id           &=
nbsp;  =20
serial           &nb=
sp;   =20
not null,<BR>    event_description    &n=
bsp;=20
char(255)           =
         =20
,<BR>   =20
person_id           =
  =20
serial           &nb=
sp;           =20
,<BR>    primary key (event_id),<BR>    forei=
gn=20
key  (person_id)<BR>       references pe=
rson=20
(person_id)<BR>);</FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT> </DIV>
<DIV><FONT face=3DArial size=3D2>regards</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Jai</FONT></DIV></BODY></HTML>

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Re: [SQL] null foreign key column

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