Gegraphic Query

Hi

I have two tables: first "points" with id, latitude and longitude, second
"zipcodes" with id, zip, latitude, longitude. Id like to ask the query which
would give me a table with id, zip where id is the id of the point from
points table and zip is the closest zip to this point.

I know that i should use something like
min(abs(point.longitude-zipcodes.longitude)) but i have no clue how to as
the full query.

Thank you very much for your help.