weird GROUP BY error

Hi All!

I experienced the strange error when running a simple query.

1) I have the following tables :
wsdb=# \d slit_data
Table "public.slit_data"
 Column |       Type       | Modifiers
--------+------------------+-----------
 chip   | smallint         |
 tile   | smallint         |
 slit   | smallint         |
 id     | integer          |
 cx     | double precision |
....

wsdb=# \d gems_spec
           Table "public.gems_spec"
  Column   |         Type          | Modifiers
-----------+-----------------------+-----------
 tile      | smallint              |
 chip      | smallint              |
 id        | integer               |
 priority  | smallint              |
....

2) When I run the query like this
wsdb# SELECT id,slit,tile,chip FROM slit_data LEFT JOIN gems_spec
USING(id,tile,chip) WHERE cx>0.5 ORDER BY priority,id;

it runs smoothly,  but when I run the same query with aggregate, I get the
error:

wsdb=# SELECT count(*) FROM slit_data LEFT JOIN gems_spec
USING(id,tile,chip) WHERE cx>0.5 ORDER BY priority,id;

ERROR:  column "gems_spec.priority" must appear in the GROUP BY clause or be
used in an aggregate function

Is that normal? I really do not see the reason for the error. I even don't
use the "GROUP BY" clause. Am I wrong ?

(I'm using PG 8.1.3)

Thanks in advance for any advices.

Regards,
    Sergey


*****************************************************
Sergey E. Koposov
Max Planck Institute for Astronomy/Sternberg Astronomical Institute
Web: http://lnfm1.sai.msu.ru/~math
E-mail: math@sai.msu.ru