MySQL Query for Average of last 2 attempts

Question

I have a table:

quiz userid  attempt grade

1      3        1     33

2      3        1     67

1      3        2     90

10     3        4     20

2      3              


        

Answer 1

First you need to select just the two rows with highest attempts, which is what the subquery does, then average the grades from the derived table.

SELECT 
    AVG(grade) 
FROM (
      SELECT 
          grade 
      FROM 
          `table`
      ORDER BY attempt DESC 
      LIMIT 2
     ) t;

This will give you a result of 55.0000, which is the average of 90 and 20, the grades for the last two attempts.