Question

I have a table that list students’ grades per class.
I want a result set that looks like:

BIO...B
CHEM...C

Where the “B” and “C” are the modes for the class.
I can get a mode of all of the grades, but not sure how to get the mode per class

Answer 1

here, something like this on SQL 2005/2008:

;WITH 
  Counts AS (
    SELECT ClassName, Grade, COUNT(*) AS GradeFreq 
    FROM Scores
    GROUP BY ClassName, Grade
    )
, Ranked AS (
    SELECT ClassName, Grade, GradeFreq
    , Ranking = DENSE_RANK() OVER (PARTITION BY ClassName ORDER BY GradeFreq DESC)
    FROM Counts
    )
SELECT * FROM Ranked WHERE Ranking = 1

or perhaps just:

;WITH Ranked AS (
  SELECT 
    ClassName, Grade
  , GradeFreq = COUNT(*)
  , Ranking = DENSE_RANK() OVER (PARTITION BY ClassName ORDER BY COUNT(*) DESC)
  FROM Scores
  GROUP BY ClassName, Grade
  )
SELECT * FROM Ranked WHERE Ranking = 1