Re: partial "on-delete set null" constraint

> On 03 Jan 2015, at 18:05, Rafal Pietrak <rafal(at)ztk-rp(dot)eu> wrote:
> W dniu 03.01.2015 o 16:48, Alban Hertroys pisze:
>>> On 03 Jan 2015, at 15:20, Rafal Pietrak <rafal(at)ztk-rp(dot)eu> wrote:
>>>
> [-------------------------]
>>> Yes. This is precisely the "semantics" I'm trying to put into the schema: after a username is "released" from service, all it's messages become "from unknown user".... unless thoroughly investigated :)
>> It also makes a foreign key reference unusable: There is no unique parent record to match it to, so what exactly are you referencing?
>
> Nothing.
>
> That's precisely my point here. I'd like to have "objects" in mailboxes table left "hanging around" after it's "disconnected" from service. FK acting like a power cord of a vacuum cleaner: when in service: hooked into the wall; after that vacuum cleaner stays there, only disconnected (and the socket can be used by others).

Then you should make that reference to maildomains(domain) also NULLable. Otherwise you aren’t referencing ‘nothing’, but possibly every user in the domain (we won’t know, since NULL is ‘unknown’ after all and that could match anything).

Alban Hertroys
--
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cut the trees and you'll find there is no forest.