Hierarchical GROUP BY aggregation

Consider the schema -- Country, salesPersonName, AmountSold

We want to find out top N countries by total amount of sales. For each such top N country, we want to find the top N sales people who have done the maximum total sales.

Input

```
India abc 100
India def 250
India ijk 500
China pqr 150
China bcd 350
China bcd 100
China qwe 320
US dsv 100
US xyz 300
US asd 330
```

N = 2

Output

```
China 920 bcd 450
China 920 qwe 320
India 850 ijk 500
India 850 def 250
```

The value of N can differ from one level to next level in hierarchy. In the above example, N could be 3 at the country level (level 0) and 2 at the salesPersonName level (level 1)

The query syntax will have to be discussed to understand how to specify the different levels and N value at each level. The output format shown above is to explain concept but should be discussed as well.