oracle - SQL -- Get items responsible for top 50% of sales -

i have table this:

item_sales     item_name   sales     item_name_1 5000     ...     item_name_x 3 

what want get items represent top 50% of sales. example, if total sales 10,000, item_name_1 alone represent 50% of sales.

i can total sales with:

select sum(sales) item_sales. 

...and divide 2 how many sales 50% of sales is.

however, don't know how i'd go there getting top items represent 50% of sales.

you can using analytic functions:

select s.* (select item_name, sum(sales) sumsales,              sum(sum(sales)) on (order sum(sales) desc) cumesales,              sum(sum(sales)) on () totsales,       item_sales       group item_name      ) s (cumesales - sumsales) < 0.5 * totsales; 

the subquery calculates sales each item, 2 other values:

• the cumulative sales, highest item.
• the total sales.

the where clause gets items , include 1 passes 50% threshold.