Ntile function

The following is an example of an ntile function that divides the total sales of each city into four buckets (because there are six data points, the first two buckets each get an extra value):

SELECT city, sum(amt), ntile(4) over(ORDER BY sum(amt)) FROM sales_tbl 
GROUP BY city;
CITY        |  SUM  | NTILE 
------------+-------+------- 
Atlanta     |  6300 |     1
Boston      |  7600 |     1 
Seattle     |  8700 |     2 
Baltimore   |  9000 |     2 
Los Angeles | 14800 |     3 
New York    | 16000 |     4
(6 rows)