Re: MULTISET and additional functions for ARRAY

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?

--
Robert Haas
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