What about a 0? That seems more consistent to me. If the array is empty, its dimensions are not "NULL", meaning "unknown", but in fact zero elements, which is a known value.
They cannot be 0 because 0 is a real index. They are undefined, because an empty array has no dimensions. It is entirely possible to have a real array that starts at a lower bound of 0 (or even an upper bound of 0).
regression=# select f[0] from (select 99 || array[1,2,3] as f) as t; f ---- 99 (1 row)
regression=# create table a1 (f int[]);
CREATE TABLE
regression=# insert into a1 values('{}');
INSERT 18688045 1
regression=# update a1 set f[0] = 99;
UPDATE 1
regression=# select array_upper(f,1) from a1;
array_upper
-------------
0
(1 row)The way it works now, array_upper on a NULL array produces the same results as array_upper on an empty-but-non-null array.
Sure, and in both cases array_upper is undefined because there are no array dimensions to speak of. I guess you might argue that array_upper, array_lower, and array_dims should all produce an ERROR on null input instead of NULL. But that would have been an un-backward compatible change for array_dims at the time array_lower and array_upper were created. I don't really believe they should throw an ERROR on an empty array though.
Joe
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