Re: select array_remove(ARRAY[NULL,NULL,NULL],NULL); returns {} instead of {NULL,NULL,NULL}

"David G. Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com> writes:
> On Mon, Aug 8, 2016 at 5:51 PM, Alban Hertroys <haramrae(at)gmail(dot)com> wrote:
>> How does it now which unknown value to remove from that array of unknown
>> values? Shouldn't the result be:
>> {NULL,NULL,NULL}?

> Is this a philosophical or technical question?

> For the former I don't see why one would choose to define this function in
> any other way. If you accept that the searching value can be NULL then it
> follows that you must compare two NULLs as equal.

Strictly speaking, array_remove (and I think array_replace as well)
implements "IS NOT DISTINCT FROM" semantics rather than "=" semantics.
I dunno that we want to make the documentation use that wording though,
it'd probably confuse more people than it helped.

regards, tom lane