Rank users in mysql by their points - mysql

Question

I am trying to rank my students by their points that I've calculated before
but the problem is if students have same points they both should be in same rank
E.g
Student 1 has full points
Student 2 has full points
they both have to be rank as 1;
Here an example of my database
the query I am trying to do is (just for select then I can insert the values to my column)
SELECT a.points
count(b.points)+1 as rank
FROM examresults a left join examresults b on a.points>b.points
group by a.points;
Edit for being more clear:
Student 1 points 80
Student 2 points 77.5
Student 3 points 77.5
Student 4 points 77
their ranks should be like
Student 1 Rank 1
Student 2 Rank 2
Student 3 Rank 2
Student 4 Rank 3
my current query returns a values like
As it is missing the third rank. (because second rank has 2 values)

Answer 1

This is just a fix of Gordon solution using variables. The thing is your rank function isnt the way rank should work. (student 4 should be rank 4)
SQL Fiddle Demo You can add more student to improve the testing.
select er.*,
(#rank := if(#points = points,
#rank,
if(#points := points,
#rank + 1,
#rank + 1
)
)
) as ranking
from students er cross join
(select #rank := 0, #points := -1) params
order by points desc;
OUTPUT
| id | points | ranking |
|----|--------|---------|
| 1 | 80 | 1 |
| 2 | 78 | 2 |
| 3 | 78 | 2 |
| 4 | 77 | 3 |
| 5 | 66 | 4 |
| 6 | 66 | 4 |
| 7 | 66 | 4 |
| 8 | 15 | 5 |

Answer 2

You want a real rank, which is calculated by the ANSI standard rank() function. You can implement this in MySQL using this logic:
select er.*,
(select 1 + count(*)
from examresults er2
where er2.points > er.points
) as ranking
from exampleresults er;
For larger tables, you can do this with variables, but it is a rather awkward:
select er.*,
(#rank := if(#rn := #rn + 1 -- increment row number
if(#points = points, #rank, -- do not increment rank
if(#points := points, -- set #points
#rn, #rn -- otherwise use row number
)
)
)
) as ranking
from examresults er cross join
(select #rn := 0, #rank := 0, #points := -1) params
order by points desc;

Answer 3

this query achieve what do you want:
SELECT student_id , points, (select count(distinct(points))+1 as rank
from examresults internal
where internal.points > external.points order by points)
FROM examresults external
group by student_id