General rule of thumb when you're not sure of a design - create the tables you think are correct. Then write queries to answer the questions you have about the...

What does the raw data look like? The results of a Matrix are useless if you're trying to create a chart - you need the unpivoted data.

That looks more like the underlying table is set up wrong. Either that or your example is misleading.
If your table is set up wrong, a query like this might...

Jeff,
I would model it like this:
Person--(1,M)--FoodAllergy--(M,1)--FoodItem--(1,M)--Ingredient_In--(M,1)--Recipe
Person has FoodAllergy to FoodItem which can be an Ingredient in one or more Recipes.

The structure of a junction table,...

Probably the easiest way is to stack the tablixes on top of one another and set the visibility property based on the parameter value.

Jack,
Luis' answer fixed it. This is the query I ended up using that worked for me:
SELECT   candidate_id, first_name, last_name
FROM    Candidate AS c
WHERE   (NOT...

Super cool, Luis! Many graces!
This worked:
SELECT   candidate_id, first_name, last_name
FROM    Candidate AS c
WHERE   (NOT EXISTS
          (SELECT   1 AS Expr1
           FROM    Candidate...

Oh, super handy! Thanks for asking... I was playing with the SSRS end of this... Getting the count of selected values is easy in SSRS. It's the passing that back...

Jack,
I asked a question about how to do this in another forum. Check this out:
https://www.sqlservercentral.com/Forums/1922517/EXISTS-ALL#bm1922645

Jason,
Wow. I'll take a while to get my head around all this. Say I'm using SSRS as a front end to this - Essentially "Show me all candidates that...

Exercised my Google-fu... Relational division, anybody?
https://stackoverflow.com/questions/15977126/select-rows-that-match-all-items-in-a-list

I'm working on it... In T-SQL, it would be like this:
(Yes, I'm aware that this table design of Candidate is silly!!!)
.
CREATE TABLE Candidate(
    CandidateID INT...

One thing to do is go find the local SQL Server User Group and go to the meetings. Open positions are often announced at the beginning of each meeting. If...