Re: array_length(anyarray)

On 19 December 2013 08:05, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
>
>
>
> 2013/12/19 David Fetter <david(at)fetter(dot)org>
>>
>> On Wed, Dec 18, 2013 at 09:27:54PM +0100, Marko Tiikkaja wrote:
>> > Hi,
>> >
>> > Attached is a patch to add support for array_length(anyarray), which
>> > only works for one-dimensional arrays, returns 0 for empty arrays
>> > and complains if the array's lower bound isn't 1. In other words,
>> > does the right thing when used with the arrays people use 99% of the
>> > time.
>>
>> +1 for adding this.
>
>
> +1
>

I think that having 2 functions called array_length() that each behave
differently for empty arrays would just lead to confusion.

The SQL standard defines a function called cardinality() that returns
the number of elements of a collection (array or multiset), so why
don't we call it that?

> length should be irrelevant to fact so array starts from 1, 0 or anything
> else

Yes, this should just return the number of elements, and 0 for an empty array.

How it should behave for multi-dimensional arrays is less clear, but
I'd argue that it should return the total number of elements, i.e.
cardinality('{{1,2},{3,4}}'::int[][]) = 4. That would make it
consistent with the choices we've already made for unnest() and
ordinality:
- cardinality(foo) = (select count(*) from unnest(foo)).
- unnest with ordinality would always result in ordinals in the range
[1, cardinality].

Regards,
Dean