Difficult query in either Linq To Sql or SQL - sql

Question

I've been working on this for 2 days and I can't figure it out. I'm hoping someone smarter than me will give this a go.
Let's say I have the following tables:
Rating:
Id | Name
1 | A
2 | B
3 | C
4 | D
5 | E
Inspection:
Id | Date (mm/dd/yyyy)
1 | 01/04/2012
2 | 04/04/2012
3 | 28/03/2012
4 | 04/04/2012
Observation:
Id | InspectionId | RatingId
1 | 2 | 3
2 | 1 | 2
3 | 4 | 3
4 | 2 | 1
5 | 3 | 3
6 | 1 | 2
I want the query to return:
RatingName | Date(mm/dd/yyyy) | ObservationCount
A | 01/04/2012 | 0
B | 01/04/2012 | 1
C | 01/04/2012 | 1
D | 01/04/2012 | 0
E | 01/04/2012 | 0
A | 04/04/2012 | 1
B | 04/04/2012 | 0
C | 04/04/2012 | 2
D | 04/04/2012 | 0
E | 04/04/2012 | 0
A | 28/03/2012 | 0
B | 28/03/2012 | 0
C | 28/03/2012 | 1
D | 28/03/2012 | 0
E | 28/03/2012 | 0
So I need the number of Observations for each rating for each date. And yes I need to have the records which return 0 Observations because I'm using this data in a stacked chart and without them it throws an error. I've managed to get the above table but without the records that return 0 Observations with the following Linq To Sql query, but from this point I get stuck.
MyDataContext DB = new MyDataContext();
var data =
(from r in DB.Ratings
join o in DB.Observations on r.Id equals o.RatingId into ro
from observation in ro.DefaultIfEmpty()
join i in DB.Inspections on observation.InspectionId equals i.Id into roi
from q in roi.DefaultIfEmpty()
group q by new { Name = r.Name, Date = q.Date } into grouped
select
new
{
RatingName = grouped.Key.Name,
Date = grouped.Key.Date,
ObservationCount = grouped.Count(x => x != null)
}).OrderBy(x => x.Date);
I would appreciate an answer in either Linq To Sql or just plain old SQL, thanks!

Answer 1

You should try a CROSS JOIN on the two reference tables, and then OUTER JOIN back to your 'data' table - and then check whether the Observation is null... then group and sum!
SELECT
[Name],
[Date],
SUM([Exists])
FROM
(
SELECT
name,
[Date],
CASE WHEN o.Id IS NULL THEN 0
ELSE 1
END as [Exists]
FROM
Rating r CROSS JOIN
Inspection i
LEFT OUTER JOIN Observation o
ON o.RatingId = r.Id AND o.InspectionId = i.Id
) as [source]
GROUP BY [Name], [Date]
ORDER BY
[Date],
name
Translating to LINQ would be a similar two-step process - get the inner result set (checking whether observation is NULL), before grouping and summing.