Row_Number Function

i want distinct rows from the table
i want to use "Row_Number" function with this
so
how can i use "Row_Number" function when distinct keyword is used
so i get the distinct rows as well as Row Numbers

suppose my table is as below:

Row Nos id class name

11mca sasfdfj
21mca jklj
32mca jljlj
42mca jkljljl
53mcs gghgh
64mca gghgh
73mcs gghghUsing distinct keyword is equivalent to using group by specifying all fields, so you can just use group by, and specify ROW_NUMBER as usual