From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Peter Eisentraut <peter_e(at)gmx(dot)net> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Itagaki Takahiro <itagaki(dot)takahiro(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: MULTISET and additional functions for ARRAY |
Date: | 2010-11-16 22:50:56 |
Message-ID: | 8140.1289947856@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> On fre, 2010-11-12 at 09:44 -0500, Tom Lane wrote:
>> But I'm still not convinced that this feature is useful enough to
>> justify the implementation effort. AFAICS there's nothing here that
>> you couldn't get with some non-default operators on regular arrays,
> Unique constraints would behave differently for arrays and multisets.
> But I suppose you could get something similar with exclusion constraints
> nowadays. But not for primary keys.
> Foreign keys also don't work easily with nondefault operators.
> JOIN / USING doesn't work.
> ORDER BY would work but look ugly. And such coding where you'd have to
> remember the nondefault operator everywhere would also be error prone.
Hmm. Those are perhaps good arguments --- but you can't get any of
those behaviors unless multisets are distinct types. The implementation
proposed upthread where they're arrays with a special typmod isn't going
to support this.
regards, tom lane
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