| From: | Hannu Krosing <hannu(at)trust(dot)ee> |
|---|---|
| To: | Jan Wieck <wieck(at)debis(dot)com> |
| Cc: | PostgreSQL HACKERS <pgsql-hackers(at)postgreSQL(dot)org> |
| Subject: | Re: [HACKERS] RI generic trigger procs |
| Date: | 1999-09-29 20:37:50 |
| Message-ID: | 37F2789E.FD90C49F@trust.ee |
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| Lists: | pgsql-hackers |
Jan Wieck wrote:
>
> Any combination of attributes in a table referenced to by one
> or more FOREIGN KEY ... REFERENCES constraint of another
> table shall have a UNIQUE and NOT NULL constraint.
...
> So we assume here that any PK is unique and cannot contain NULL's.
What is the reasoning behind requiring this ?
I can't see anything that would mandate this -
* NULLs are'nt equal anyway and ar even disregarded under your
current description.
Or are you just protecting yourself against the case where the
foreign key field is set to null - could this be handled the
same as deleting for cascaded constraints ?
* UNIQUE would save us the check for existing other possible
referenced values - is this mandated by SQL spec ?
-------------
Hannu
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