subselect and left join not working?

<div style="font-family:arial,helvetica,sans-serif;font-size:10pt;color:#000000;"><div style="font-family: Courier
New,courier,monaco,monospace,sans-serif;">Hi,<br /><br />I am using postgres 8.4 and I am having problems doing a very
simplequery:<br /><br />select zona_id from zonas where zona_id not in (select zona_id from usuarios where per_id
=2)<br/><br /> but I get no records in return. <br /><br />The problem is that, if I I break down the quey, I get:<br
/><br/>select zona_id from zonas <br /><br />"A"<br />"B"<br />"C"<br />"D"<br />"E"<br />"F"<br />"FCHIH"<br
/>"FCOAH"<br/>"DGO"<br />"T"<br />"FGTO"<br />"FGRO"<br />"FQRO"<br />"FHGO"<br />"JAL"<br />"MOR"<br />"FPUE"<br
/>"FQROO"<br/>"FSLP"<br />"F VER"<br />"FYUC"<br />""<br /><br />select zona_id from usuarios where per_id =2<br /><br
/>"E"<br/>"F"<br />"FCHIH"<br />"JAL"<br />"FPUE"<br />"F VER"<br />"C"<br />"D"<br />"A"<br />""<br /><br />but with
<br/><br />select zona_id from zonas where zona_id not in (select zona_id from usuarios where per_id =2)<br /><br />I
dont'get records when I am expecting to see this:<br /><br /> "B"<br /> "FCOAH"<br /> "DGO"<br /> "T"<br /> "FGTO"<br
/>"FGRO"<br /> "FQRO"<br /> "FHGO"<br /> "MOR"<br /> "FQROO"<br /> "FSLP"<br /> "FYUC"<br /> ""<br /><br />What's
wrong?Please help. Any clues?<br /><br /><br />---<br />It also does not work a left join on 'zonas'. Some 'zonas' are
designatedto some users but in my case is not wroking:<br /><br />t1<br />usr    zone<br />1       A<br />2       C<br
/>3      D<br /><br />t2<br />zone<br />A<br />B<br />C<br />D<br />E<br /><br />I want to see<br />zone    usr<br
/>A       1<br />B<br />C        2<br />D        3<br />E<br /></div></div>