Rank users in mysql by their points

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

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 2

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 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