percentiles from histogram data

Question

The following table captures student grade data over a number of exams.

CREATE TABLE grades
AS
  SELECT name, exams, grade_poor, grade_fair, grade_good, grad         


        

Answer 1

SELECT name, exams,
       CASE WHEN 0.5 * exams <= grade_poor
                THEN 'grade_poor'
            WHEN 0.5 * exams <= grade_poor + grade_fair
                THEN 'grade_fair'
            WHEN 0.5 * exams <= grade_poor + grade_fair + grade_good
                THEN 'grade_good'
            ELSE 'grade_vgood' END AS median_grade;

This rounds ties down so neha will score "grade_fair" and radha will score "grade_good". If you want to round up, change <= into <.