offset and limit in update and subselect

Hi,

It appears that limit and offset do not work in a subselect such as:
update my_table set my_col = new_val where oid = (select oid from 
my_table offset row_number limit 1);

Basically, I need to update rows by offset from the beginning of the 
table.  Even nicer would be
update my_table set my_col = new_val offset row_number limit 1;

But this is not supported either.

Tim

-- 
Timothy H. Keitt
Department of Ecology and Evolution
State University of New York at Stony Brook
Phone: 631-632-1101, FAX: 631-632-7626
http://life.bio.sunysb.edu/ee/keitt/