Self-Referencing

Hello,
 I have a feeling this isn't going to make much sense, but I'm gonig to try anyway.
 What I'd like to do is be able to refer to an outer-SELECT from an inner-SELECT. I hope this makes sense.
 I need to be able to refer to the row that's being processed in a SELECT. I'm going to use the idea of 'this'
referringto the row that's currently being processed. Here's the example of what I'd like:
 
 SELECT   building_id,   num_buildings,   (     SELECT count( building_id )     FROM   building_portals     WHERE
building_id= THIS.building_id   ) FROM buildings;
 
 Am I making things too complicated, and if so will somebody *PLEASE* tell me the easier way to do this. Thanks.

-- Dave