Thread: BUG #4956: Array Construct array() returning blank result

The following bug has been logged online:

Bug reference:      4956
Logged by:          Niranjan Pandit
Email address:      niranjan81@gmail.com
PostgreSQL version: 8.4
Operating system:   Windows Vista Ultimate
Description:        Array Construct array() returning blank result
Details:

Hi,
I simply wanted to accumulate result of a subquery in to an array, so I did
select array(select userid from user where <some condition>);

Only when the condition gets evaluated to true with at least 2 columns with
varying values the array gets constructed, in all other cases what we get is
a complete blank output. the label of the result is as usual as ?column? but
there is absolutely nothing in the cell below the label.

I am sorry if I am repeating something already known to mankind :-) but
after a lot search I could not get anything on it on the net.

Thanks in advance.

Best Wishes.

"Niranjan Pandit" <niranjan81@gmail.com> writes:
> Only when the condition gets evaluated to true with at least 2 columns with
> varying values the array gets constructed, in all other cases what we get is
> a complete blank output. the label of the result is as usual as ?column? but
> there is absolutely nothing in the cell below the label.

Hmm, seems to work for me:

regression=# select array(select unique1 from tenk1 where unique2 < 2);
  ?column?
-------------
 {8800,1891}
(1 row)

regression=# select array(select unique1 from tenk1 where unique2 < 1);
 ?column?
----------
 {8800}
(1 row)

regression=# select array(select unique1 from tenk1 where unique2 < 0);
 ?column?
----------
 {}
(1 row)

Pre-8.3 PG releases would return NULL instead of an empty array in the
last case, but 8,4 should not.  If you're seeing differently, we'll
need a self-contained test case.

            regards, tom lane