Re: Inconsistent behavior on Array & Is Null?

Josh Berkus wrote:
> 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