What is the specificity limit of EntityFieldQuery / fieldCondition?
Yes, it is possible.

The second question is different, what you are describing is exactly what EFQ can do.

Something like this should work:

-&gt;fieldCondition('field_answer_quiz', 'nid', $nid)


The column names in the field tables are a combination of the field name and the column name, you need to split that up like the above example.