Re: Supporting NULL elements in arrays

On Tue, Nov 08, 2005 at 07:21:34PM -0500, Tom Lane wrote:
> I wrote:
> > ... the most straightforward thing to do is define an empty element
> > as meaning a NULL. But this might be objected to on a couple of grounds:
> I just thought of another, potentially fatal objection: it's ambiguous
> whether '{}'::text[] should be taken to mean an empty (zero-length)
> array or an array containing a single NULL element.

To take another perspective on this, though - it isn't possible to have
NULL array elements right now, therefore, there is no precident, and who
is to say that {NULL} <> {}?

For example:

vhosts=> select ('{1, 3}'::text[])[4];
text
------

(1 row)

vhosts=> select ('{}'::text[])[4];
text
------

(1 row)

Perhaps NULL at end of array never needs to be stored, and arrays can
be considered to have an infinite number of NULL values at the end?

For array operations that require a length, such as cross-product, or
whatever, the 'length' of the array, would be the number of elements
before the infinite number of NULL values at the end.

Cheers,
mark

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