select * from 
  (select customer_id as cust_id, sum(sales_amt) as 
  cust_sales, round(100 * CUME_DIST() over(order by 
  sum(sales_amt) asc)) as cust_percentile
  from sales group by customer_id)

where cust_percentile > 85
order by cust_percentile desc;

CUST_ID          CUST_SALES            CUST_PERCENTILE
------------     -----------------     ------------------------
133461           2175523               100

270570           1805256               99
160160           1801329               98
......           .......               ..
......           .......               ..
133508           1124910               86