Thread: BUG #8393: "ERROR: failed to locate grouping columns" on grouping by varchar returned from function

The following bug has been logged on the website:

Bug reference:      8393
Logged by:          Evan Martin
Email address:      postgresql@realityexists.net
PostgreSQL version: 9.2.4
Operating system:   Windows 7 x64 SP1
Description:

version(): PostgreSQL 9.2.4, compiled by Visual C++ build 1600, 64-bit


Run the following:


CREATE OR REPLACE FUNCTION test_group_by()
RETURNS TABLE (my_col varchar(5))
AS $BODY$
    SELECT 'hello'::varchar(5);
$BODY$ LANGUAGE sql STABLE;


SELECT my_col
FROM test_group_by()
GROUP BY 1;




Expected result:


'hello'


Actual result:


ERROR:  failed to locate grouping columns


Interestingly, if the function is marked "VOLATILE" it works. Casting the
result to "text" also makes it work.

postgresql@realityexists.net writes:
> CREATE OR REPLACE FUNCTION test_group_by()
> RETURNS TABLE (my_col varchar(5))
> AS $BODY$
>     SELECT 'hello'::varchar(5);
> $BODY$ LANGUAGE sql STABLE;

> SELECT my_col
> FROM test_group_by()
> GROUP BY 1;

> ERROR:  failed to locate grouping columns

Fixed in our git tree; thanks for the report!

As a workaround in this particular case, you could just not bother with
marking the specific length of the varchar constant.  The function
definition essentially ignores the length, storing only "varchar" as the
result column type, and it's the discrepancy between that and the
declaration of the constant that's tickling the bug.

            regards, tom lane