-- The query below shows first four values (sales) from 
-- each location using the analytic function 
-- DENSE_RANK().

-- The DENSE_RANK() can be used to get equal sample
-- from a set of values (using four in query below
-- from each location).

SELECT
 location_code,
 sales 
FROM
(SELECT
  qtab.loc_cd  location_code,
  qtab.sales,
  DENSE_RANK() OVER
   (PARTITION BY qtab.loc_cd
        ORDER BY qtab.sales) denserank_sales
 FROM
  (SELECT 'A1' loc_cd, 111 sales FROM DUAL UNION 
   SELECT 'A1' loc_cd, 211 sales FROM DUAL UNION
   SELECT 'A1' loc_cd, 321 sales FROM DUAL UNION
   SELECT 'A1' loc_cd, 101 sales FROM DUAL UNION
   SELECT 'A1' loc_cd, 432 sales FROM DUAL UNION
   SELECT 'A1' loc_cd, 543 sales FROM DUAL
   UNION
   SELECT 'B1' loc_cd, 100 sales FROM DUAL UNION
   SELECT 'B1' loc_cd, 210 sales FROM DUAL UNION
   SELECT 'B1' loc_cd, 320 sales FROM DUAL UNION
   SELECT 'B1' loc_cd, 110 sales FROM DUAL UNION
   SELECT 'B1' loc_cd, 430 sales FROM DUAL UNION
   SELECT 'B1' loc_cd, 540 sales FROM DUAL
  ) qtab
)
WHERE denserank_sales < 5;


LOCATIOC_CODE      SALES
------------- ----------
A1                   101
A1                   111
A1                   211
A1                   321
B1                   100
B1                   110
B1                   210
B1                   320