SELECT COUNT(*) as customer_count FROM customer_table c
WHERE EXISTS(
SELECT 1 FROM locations_table s
WHERE ST_Distance_Sphere(s.the_geom, c.the_geom) < 10000
)

create table customer (
  loc real,
  name text
);
create index on customer(loc);
create table location (
  loc real,
  name text
);
create index on location(loc);
insert into customer values (1,'c1'), (2,'c2');
insert into location values (1.1, 'l1'), (1.2, 'l2');
select cat, count(*) from (
  select bussiness, "name", dist ,
    case when dist>.5 then 'far'
         when dist > .11 then 'nearby'
         else 'local' end cat
  from (
    select l.name bussiness, c.name "name", abs(l.loc - c.loc) dist -- Use your ST_Distance_Sphere
    from location l, customer c
    where abs(l.loc - c.loc)< .89 -- ST_DWithin is here
  ) foo
) bar
group by cat

CREATE OR REPLACE VIEW b1 as
SELECT ST_Buffer(the_geom,10000) as geom, store_name, fid
FROM stores;

CREATE OR REPLACE VIEW r2 as
SELECT ff.fid, ff.store_name, ST_Difference(ff.the_geom, g.the_geom) as new_geom
FROM b2 ff
JOIN b1 g ON (g.fid= ff.fid)
GROUP BY ff.fid, ff.store_name, g.the_geom, ff.the_geom;