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@xxxxxxxxxx