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)