[Solved] Get Rank based per row of a student score on a subject in sql server

How to optimize this SQL query?

In case you have your own slow SQL query, you can optimize it automatically here.

For the query above, the following recommendations will be helpful as part of the SQL tuning process.
You'll find 3 sections below:

  1. Description of the steps you can take to speed up the query.
  2. The optimal indexes for this query, which you can copy and create in your database.
  3. An automatically re-written query you can copy and execute in your database.
The optimization process and recommendations:
  1. Avoid Selecting Unnecessary Columns (query line: 2): Avoid selecting all columns with the '*' wildcard, unless you intend to use them all. Selecting redundant columns may result in unnecessary performance degradation.
  2. Create Optimal Indexes (modified query below): The recommended indexes are an integral part of this optimization effort and should be created before testing the execution duration of the optimized query.
Optimal indexes for this query:
CREATE INDEX tbl_result_idx_student_id ON dbo.tbl_result (student_id);
The optimized query:
SELECT
        stu.*,
        (SELECT
            TOP 1 +DENSE_RANK() OVER (PARTITION 
        BY
            [tbl_result].score 
        ORDER BY
            [tbl_result].score DESC) AS ranking 
        FROM
            [dbo].[tbl_result] 
        WHERE
            [dbo].[tbl_result].[student_id] = stu.[student_id]) AS Rank 
    FROM
        [dbo].[tbl_result] stu 
    WHERE
        stu.[student_id] = 'R135722F'

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* original question posted on StackOverflow here.