Re: MULTISET and additional functions for ARRAY

On Fri, Nov 12, 2010 at 12:53:09AM -0500, Robert Haas wrote:
> On Fri, Nov 12, 2010 at 12:21 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> >> On Thu, Nov 11, 2010 at 10:02 AM, Itagaki Takahiro
> >> <itagaki(dot)takahiro(at)gmail(dot)com> wrote:
> >>> If we reuse type IDs of arrays for multisets, the multisets would
> >>> have some special typmod. For example, typmod = 0 means multiset,
> >>> and positive value means array with max cardinality. Note that
> >>> the SQL standard doesn't mention about multi-dimensional arrays.
> >>> So, we can use typmod = -1 as a free-size and free-dimensional
> >>> array for backward compatibility.
> >
> >> I would really like to see us fix our type system so that it doesn't
> >> require this type of awful hack.  But maybe that's asking too much of
> >> a patch to implement this feature.
> >
> > The problem is not with the type system: as long as you give multisets
> > different type OIDs from arrays, everything will work fine.  It will
> > absolutely not work to try to use typmod to make the behavior vary
> > like that ... but Itagaki-san knew that already.
>
> And thus you must create a THIRD copy of every entry in pg_type. That
> doesn't qualify as a problem?

Yes, and I've started a separate thread on this along with a page on
the wiki.

Cheers,
David.
--
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