Selecting Alternatives

[seascope]

I see that there is the ability to select Excluded and to select Alternatives. But this doesn't help me.

To reduce it to a simple two set analysis 

set A: 40 students

set B: 20 different subjects

Each student can study as many subjects as he/she wishes. 

If I select one student from A I can see all the subjects that he/she takes. If I then either select Alternative or Excluded in the student set  I can see all the subjects that everyone else takes - I want to be able to identify the subjects that the student does not take.  I'm sure its very simple to do, but how do i do it?

[Or]

Select all on Students, then Select Excluded on Subjects.

[vinieme12]

please post some sample data

[seascope]

Thanks - I have tried this and it gives me part of what I want.

How do I expand this to show the Subjects that student A doesn't take but but student B does? 

[marcus_sommer]

I'm not sure if I comprehend your question right but I could imagine it's not a question of selecting values else of the availability of them. This means if student X takes 4 from the 20 subjects are there 20 records with 4 TRUE and 16 FALSE entries or are there just 4 records. I assume the last scenario is the reality and then there is nothing what could be selected because it's NULL which isn't stored in any way and therefore not accessible or selectable.

At least not directly - in some cases/requirements it's possible to bypass it with any indirect approaches. But it could become complex and slow and has usually also side-effects. In many cases it would be easier and in the end more suitable to populate missing data within the script. In your case it might be something like:

t: load distinct Student from X; join(t) load distinct Subject from Y;

to create an empty cartesian product and all existing Student+Subject combinations are mapped against it (mapping is faster as a join and provides a default-value for non-matching which a join couldn't do else what would require a following load).

- Marcus