Ron Johnson <ron(dot)l(dot)johnson(at)cox(dot)net> writes:
> I think he's asking why:
> select timestamp with time zone '2007-01-01'
> at time zone 'America/Los_Angeles';
> returns a different value than
> select timestamp '2007-01-01'
> at time zone 'America/Los_Angeles';
Those are transformations in opposite directions; see the manual.
regards, tom lane