Question

I have a table of students that has some data about whether or not they attent a tutorial etc. There is an extract below.

|   id |   studentid | name |  present | 
|   1  |   111       | John |       1  | 
|   2  |   222       | Kate |       0  | 
|   3  |   333       | Matt |       1  | 
|   4  |   111       | John |       0  | 
|   5  |   111       | John |       1  | 

I can do a count to say when eg studentid=111 and present = 1 and when studentid=111 and present = 0.
But I can’t work out these two things.

i. Can I do just one count query rather than doing a seperate count for each?
Currently with my two seperate queries I am getting eg

studentid=111 and present = 1

| name |  present | 
| John |       12 | 

studentid=111 and present = 0

| name |  absent | 
| John |       4 | 

But I would ideally like

| name |  present |  absent | 
| John |       12 |       4 | 

ii.I want to see those students who have been to less than 75% of the classes. I have done some reading about the avg function however I am not sure how to implement something for this?

Answer 1

To list the students that have been to less than 75% of classes:

SELECT
  studentid,
  name, 
  SUM(present) AS present,
  SUM(present = 0) AS absent
FROM your_table
GROUP BY studentid, name
HAVING present < .75 * (present+absent)