How do I find the first, second, and third largest marks obtained for a particular subject in mySQL?

 To find the first, second, and third largest marks obtained in a particular subject using MySQL, you can use the LIMIT clause combined with ORDER BY to sort the marks in descending order. Here are a few approaches to achieve this:

Assumptions:

• You have a table named marks (or any name you're using).
• The table has columns student_id, subject, and marks, where marks represent the score obtained in a particular subject.

Let's assume you're interested in the subject 'Math'. Here's how to find the first, second, and third largest marks:

1. Using LIMIT and OFFSET

-- First largest mark
SELECT marks
FROM marks
WHERE subject = 'Math'
ORDER BY marks DESC
LIMIT 1;

-- Second largest mark
SELECT marks
FROM marks
WHERE subject = 'Math'
ORDER BY marks DESC
LIMIT 1 OFFSET 1;

-- Third largest mark
SELECT marks
FROM marks
WHERE subject = 'Math'
ORDER BY marks DESC
LIMIT 1 OFFSET 2;

In this approach:

• The first query gets the highest mark.
• The second query skips the first record using OFFSET 1 and gets the second highest.
• The third query skips the first two records using OFFSET 2 and retrieves the third highest.

2. Using DISTINCT with LIMIT

If you want to account for possible duplicate scores (i.e., the same score appearing more than once), you can use DISTINCT to eliminate duplicates. This is useful when you want the unique largest marks.

-- First largest mark
SELECT DISTINCT marks
FROM marks
WHERE subject = 'Math'
ORDER BY marks DESC
LIMIT 1;

-- Second largest mark
SELECT DISTINCT marks
FROM marks
WHERE subject = 'Math'
ORDER BY marks DESC
LIMIT 1 OFFSET 1;

-- Third largest mark
SELECT DISTINCT marks
FROM marks
WHERE subject = 'Math'
ORDER BY marks DESC
LIMIT 1 OFFSET 2;

3. Using ROW_NUMBER() (MySQL 8.0+)

If you're using MySQL 8.0 or later, you can use the ROW_NUMBER() window function to assign row numbers to the scores ordered by their value. This method will give you more flexibility in handling duplicates and complex queries.

WITH RankedMarks AS (
    SELECT marks,
           ROW_NUMBER() OVER (ORDER BY marks DESC) AS rank
    FROM marks
    WHERE subject = 'Math'
)
SELECT marks
FROM RankedMarks
WHERE rank = 1  -- First largest
   OR rank = 2  -- Second largest
   OR rank = 3; -- Third largest

In this query:

• The ROW_NUMBER() function assigns a rank to each mark based on the descending order.
• The outer query filters the results to return only the first, second, and third largest marks.

Conclusion:

• For simple queries, use LIMIT with OFFSET to find the first, second, and third largest marks.
• For handling duplicates, use DISTINCT to ensure unique results.
• For more complex or optimized queries (especially in MySQL 8.0+), you can use window functions like ROW_NUMBER() to rank and filter the marks.