Row_number() function is used to generate row number to rows based on the column which is ordered

What if you want to generate row number without ordering any column

Here is the method (Consider Suppliers table from northwind database)

1 Assign dummy column with literal 0 and order it by that column

select row_number() over(order by order_col),companyname,address from 
(
        select companyname,address,0 as order_col from northwind..Suppliers
) as t

2 Assign dummy column with literal 0 directly on the Order by clause

select row_number() over(order by (select 0)),companyname,address from northwind..Suppliers

Also refer Multipurpose Row_Number() Function