Fwd: how to write the sql if i want to find a geometry's d-distance neighbors?

I can't mail it to: postgis-users(at)postgis(dot)refractions(dot)net
so could administrator forword this mail to them? thanks!

From: sunpeng <bluevaley(at)gmail(dot)com>
Date: 2010/9/12
Subject: how to write the sql if i want to find a geometry's d-distance
neighbors?
To: postgis-users(at)postgis(dot)refractions(dot)net

Hi,
I've the following table,and has created the index on uid and location;
CREATE TABLE points
(
location geometry, //assume it's a 2-dimension point
uid integer
)

Now, I've a point P with uid= 12345, and want to find the neighbors which
are within 20, how to write the sql?Is this right?
select st_astext(location)
from points a, points b
where b.rid = 12345 and ST_DWithin(a.the_geom, b.the_geom, 20)

or use st_buffer? which one is more efficient ?

Thanks!