Re: array_length()

>> There is a tiny problem with this implementation: It returns null for an
>> empty array, not zero.  This is because array_lower and/or array_upper
>> return null for an empty array, which makes sense for those cases.  We
>> could fix this by putting a coalesce around the expression, but since
>> the array functions return null for all kinds of error cases, this might
>> mask other problems.  Or we move to a C implementation.

Hmm... the problem is that an empty array is really zero-dimensional.
So for what values of the second argument ought we to return 0?

It certainly seems inconsistent to say that array_length({}, 6) = 0
and array_length({1}, 6) is null.

We do need a good way to test for an empty array, though.  Right now I
think the best ways is array_ndims(x) IS NULL (should it return 0
rather than NULL on an empty array?).

> Basic functionality like this shouldn't be implemented as a SQL function
> anyway.  People don't expect that some built-in functions should be
> several orders of magnitude slower than other built-in functions of
> apparently similar complexity.

C implementation attached.

...Robert