Bug on complex join

Hi!

   I am continuing playing with the query (I reduced it to):
SELECT  sh.distr_id , d.distr_id                                                 
   FROM central cn, shops sh, districts d                                        
      WHERE cn.shop_id = sh.shop_id                                              

and got 27963 rows. I filtered it out (with awk:) where $1 == $2 (1st
column is equal to second) and got 3104 rows.

   But the query
SELECT d.*                                                                       
   FROM central cn, shops sh, districts d                                        
      WHERE cn.shop_id = sh.shop_id AND sh.distr_id = d.distr_id                 

returned 0 rows.

   Where is the bug?

Oleg.
---- 
    Oleg Broytmann     http://members.xoom.com/phd2/     phd2@earthling.net
           Programmers don't die, they just GOSUB without RETURN.