| From: | Dmitry Tkach <dmitry(at)openratings(dot)com> |
|---|---|
| To: | vernonw(at)gatewaytech(dot)com |
| Cc: | pgsql-sql(at)postgresql(dot)org |
| Subject: | Re: null foreign key column |
| Date: | 2003-02-13 00:19:14 |
| Message-ID: | 3E4AE482.8000908@openratings.com |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-sql |
Vernon Wu wrote:
>12/02/2003 2:24:49 PM, Dmitry Tkach <dmitry(at)openratings(dot)com> 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.
>>>
>>>------=_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
>>>
>>><!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>
>>>
>>>------=_NextPart_000_0005_01C2D1EE.61998D70--
>>>
>>>
>>>
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>>
>>
>
>
>
>
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