title: SQL Query help - Percentiles
body: <p>I have a single table with 2 columns. </p>
  
  <h2>Column</h2>
  
  <p>Student ID 
  Course Id</p>
  
  <p>Both these columns have many to many relationships with each other. 
  I want to find out - 
  1. Average number of courses registered by students across the set of all students. 
  2. 90th percentile of the number of courses registered by all the students. </p>
  
  <p>I have tried this using PERCENT_DISC() but somehow I have not been able to figure out.
  Can anyone help me with this query ?</p>