ASP.NET Chart for Grades Distribution - asp.net

Question

I'd like to show an ASP.NET Chart control that shows a distribution of grades.
It should show how many students got which grade, ranging from A to F.
How do I make the chart include the grades A, B, C, D, F in the cases where no students got, say, a D letter grade? For example, I'd like the D value to to present on the X-axis, but with a student count of zero.
The data is being pulled from a database and I'm using an ObjectDataSource to bind to the chart control.
EDIT: The structure of the data is that there's a Students table and each stundent has a FirstName, LastName, and Grade.
EDIT: For the rest of the site I'm using Entity Framework with LINQ (as opposed to writing raw SQL), so, in a perfect world, the solution wouldn't involved raw SQL.

Answer 1

Is it possible to change your query includes all grades then fill in the details for each grade?
total hack - but to show you the idea as I don't know your schema
select * from
(
select 'a' Grade
union
select 'b' Grade
union
select 'c' Grade
union
select 'd' Grade
union
select 'f' Grade
) as grades g
outer join yourothertable t on g.Grade = t.Grade
Edit: After reading your edit realizing you don't want this to be a sql solution, then the choice is to take your objects and do a linq join on them to objects containing the grade.
see:
http://www.hookedonlinq.com/OuterJoinSample.ashx
use something like
public class Grade
{
public string LetterGrade;
}
populate a list of them, and do an outer join to your results from your query. Your new linq results collection is what you now databind.

Answer 2

Without know how your data is structured it's a bit difficult to give a detailed answer. Here's a way to do it using SQL Common Table Expressions (CTEs). It will organize the data so that you can easily bind it to a chart control.
This will produce a table of data as follows:
| Grade | TotalGrades |
|-------|-------------|
| A | 2 |
| B | 1 |
| C | 2 |
| D | 0 |
| E | 0 |
| F | 1 |
And here's the code:
;With Grades (Grade) as
(
SELECT 'A' Grade
UNION
SELECT 'B' Grade
UNION
SELECT 'C' Grade
UNION
SELECT 'D' Grade
UNION
SELECT 'E' Grade
UNION
SELECT 'F' Grade
),
GradeResults (Name,Grade) as
(
SELECT 'John','A'
UNION
SELECT 'Sally','B'
UNION
SELECT 'Dave','C'
UNION
SELECT 'Charlie','C'
UNION
SELECT 'Lisa','F'
UNION
SELECT 'Russ','A'
)
SELECT a.Grade, COUNT(b.Grade) as TotalGrades FROM Grades a LEFT OUTER JOIN GradeResults b on a.Grade = b.Grade
GROUP BY a.Grade
ORDER BY a.Grade;