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
justGOSUB without RETURN.