Обсуждение: different empty array syntax requirements

How is that one pgsql build (both are 9.5.2) has different casting behavior for empty arrays:


ericmj=# select ARRAY[]::text[];
 array
-------
 {}
(1 row)

ericmj=# select (ARRAY[])::text[];
 array
-------
 {}
(1 row)


--VS--


pedcard=# select ARRAY[]::text[];
 array
-------
 {}
(1 row)

pedcard=# select (ARRAY[])::text[];
ERROR:  cannot determine type of empty array
LINE 1: select (ARRAY[])::text[];
                ^
HINT:  Explicitly cast to the desired type, for example ARRAY[]::integer[].

--
Scott Ribe
scott_ribe@elevated-dev.com
http://www.elevated-dev.com/
https://www.linkedin.com/in/scottribe/
(303) 722-0567 voice

Scott Ribe <scott_ribe@elevated-dev.com> writes:
> How is that one pgsql build (both are 9.5.2) has different casting behavior for empty arrays:
> pedcard=# select (ARRAY[])::text[];
> ERROR:  cannot determine type of empty array
> LINE 1: select (ARRAY[])::text[];
>                 ^
> HINT:  Explicitly cast to the desired type, for example ARRAY[]::integer[].

... wtf?

[ thinks for awhile ... ]

Oh!  I bet this explains it:

regression=#  select (ARRAY[])::text[];
 array
-------
 {}
(1 row)

regression=# set operator_precedence_warning = on;
SET
regression=#  select (ARRAY[])::text[];
ERROR:  cannot determine type of empty array
LINE 1: select (ARRAY[])::text[];
                ^
HINT:  Explicitly cast to the desired type, for example ARRAY[]::integer[].


The parens turn into an actual parsetree node when
operator_precedence_warning is on, and the cast-of-an-array hack doesn't
know it should look through such a node.  That's a bug.  Will fix it.

            regards, tom lane

On Apr 21, 2016, at 8:25 PM, Alvaro Aguayo Garcia-Rada <aaguayo@opensysperu.com> wrote:
>
> Looks like one has the appropiate cast operator, while the other hasn't. Have you tried doing the same, on both
server,on an empty database created from template0? 

Excellent suggestion:

pedcard=# create database test;
CREATE DATABASE
pedcard=# \c test
SSL connection (protocol: TLSv1, cipher: DHE-RSA-AES256-SHA, bits: 256, compression: off)
You are now connected to database "test" as user "admin".
test=# select (ARRAY[])::text[];
ERROR:  cannot determine type of empty array
LINE 1: select (ARRAY[])::text[];
                ^
HINT:  Explicitly cast to the desired type, for example ARRAY[]::integer[].


--
Scott Ribe
scott_ribe@elevated-dev.com
http://www.elevated-dev.com/
https://www.linkedin.com/in/scottribe/
(303) 722-0567 voice

On Apr 21, 2016, at 8:37 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> The parens turn into an actual parsetree node when
> operator_precedence_warning is on, and the cast-of-an-array hack doesn't
> know it should look through such a node.

I figured that. The mystery is why on my pg, and not on the other. I've asked the other guy to try it in a
newly-createddatabase. 

> That's a bug.  Will fix it.

OK, cool.

--
Scott Ribe
scott_ribe@elevated-dev.com
http://www.elevated-dev.com/
https://www.linkedin.com/in/scottribe/
(303) 722-0567 voice