Ranking or ordering in sql tables by partitioning

Consider we have table as follows:

Studentid	Subjectid	ObtainedScore
1	1	25
2	1	45
3	1	27
4	1	35
5	1	25
6	1	24
1	2	31
2	2	42
3	2	42
4	2	36
5	2	12
6	2	10

If we need to rank students based on their obtained score in each subject what would you write a query for. Among many way I’m illustrating following code for generating rank using row_number(), over and partition:

Syntax:
 Select studetid, subjected, obtainedscore, row_number() over ( partition by subjectid order by obtainedscore desc) as rank;

          PARTITION BY value_expression

Divides the result set produced by the FROM clause into partitions to which the ROW_NUMBER function is applied. value_expression specifies the column by which the result set is partitioned. If PARTITION BY is not specified, the function treats all rows of the query result set as a single group.
  
order_by_clause

The ORDER BY clause determines the sequence in which the rows are assigned their unique ROW_NUMBER within a specified partition. It is required.

There is no guarantee that the rows returned by a query using ROW_NUMBER() will be ordered exactly the same with each execution unless the following conditions are true.

1. Values of the partitioned column are unique.
   
2. Values of the ORDER BY columns are unique.
   
3. Combinations of values of the partition column and ORDER BY columns are unique.
   

Here partition groups the table by subjectid column and generates a rank by descending order of obtainedscore.

Output of this query would be as below

Studentid	Subjectid	ObtainedScore	rank
1	1	25	4
2	1	45	1
3	1	27	3
4	1	35	2
5	1	12	6
6	1	24	5
1	2	31	4
2	2	42	2
3	2	43	1
4	2	36	3
5	2	12	5
6	2	10	6