You can't yet... at least not with an ALTER statement. The only way to
currenty do this is by dumping the table (through pg_dump), altering the type
of the field, and then re-ipmorting the table.
Rumor has it that they are working on an ALTER statement to accomplish this
for 7.3 or 7.4.
-Dan
Quoting ameen eetemadi <ameen78101(at)yahoo(dot)com>:
> I want to change the type of a field in postgres .
> How can I do it ?