How to combine taxonomy terms? I use Taxonomy with Contextual Filter, so I can categorize content (nodes), associating taxonomy terms to each content, and filter them in a View.

I can have a node and 2 different vocabularies, lets say A = {1,2,3} and B={a,b,c}. I can, by default in Drupal usual behaviour, associate a node with multiple values of A and B, lets say that node Nid has associated 1,2 and a,b.

What I need, if it is at all possible, is to have paired associations, i.e., not only 1,2 and a,b separatedly, but in combination. Let's say
{1,a} and {2,b} and the contextual filter or equivalent, if looking for {1,a} will return the node, but if looking for {1,b} it will return nothing. Of course, {1,all} would have to return the node.

Is there such a module or behaviour in Drupal 7 ?

Note: the problem does not lie with the search or filter part. The very basic problem is how to assign a combined value to the node, in the very first place. Later I will face the problem of looking for or filtering for that data. But I don't know how to merge both taxonomy fields into one, so the node is assigned to {1,a} and not to "1" and "a" separatedly.
Do you always need to search on multiple terms at the same time? And how do you want to search, via an exposed filter or with query parameters?

In both cases you need to add references to the vocabularies A and B. 

If you want to search through an exposed filter, you can add the term name fields (with relation to the references) to the normal filter and just expose them. I'm not sure, but I think there is a way to combine this with global text search.

If you want to work with query parameters you need contextual filters. Just add a term name for both vocabularies and let them match the value of the query parameters. You can specify what results must be shown if the parameter value is 'all' for example.

I don't think you need the or operator because you mentioned you want to match on both terms at the same time. However, if you want to match on multiple combinations you might want to check this module. I haven't tested it myself, but it really saves you some time if it works. The or operator is not native in contextual filters.

Good luck! Contextual filters and references can be a real pain in the ...