在SQL中查找与每个组中的第N个值相对应的行

Question

I have a table A as follows:

name   course  grade
Bob      C1     12
Bob      C2     13
Bob      C3     23
Bob      C4     17 
James    C2     15
James    C6     27
Nick     C5    18
Nick     C1    16
Nick     C3    22
Nick     C2    32
Nick     C7    19

I want a query that can return the student name and the course number for each student corresponding to the 3rd highest grade for that student. For example, in the table above, the 3rd highest grade for Bob is 17 so the course number is C4. Also since James has fewer than 3 courses, his course should not be included in the query result. In other words, the query result should show this:

name course_id
Bob    C4
Nick   C7

What would be the query that can do that?

Answer 1

In standard SQL one would do this using window functions:

select name, course
from (
   select name, course, grade, 
          dense_rank() over (partition by name order by grade) as rnk
   from grades
) t
where rnk = 3

Online example: https://rextester.com/YOHZB50840

Online example with MySQL: https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=3f9ff551c89f6941dbf8e424e6dfda56

Answer 2

use corelated subquery and row_number analytic function which support most dbms

with cte as 
  ( select t1.* from table t1 where 
           exists ( select 1 from table t2 where t1.name=t2.name
                                 group by name 
                                 having count(distinct course)>=3
                  )
  ) , 
 cte2 as 
  (
select * ,row_number() over(partition by name order by grade asc) rn 
from cte
  ) select * from cte2 where rn=3

Answer 3

You can try using row_number()

    select name, course
    from (
       select name, course, grade, 
              row_number() over (partition by name order by grade desc) as rn
       from grades
    ) t where rn = 3