Database management system short questions and answers page contain 5 questions from chapter Relational DBMS. Each objective question has 4 possible answers. Choose your answer and check it with the given correct answer.
(21)
The set of attributes X ⊆ Schema (R) is a super key for relation schema R only if :
[A]
For all relations r over R the number of tuples in projection over X of r is the same as the number of tuples in r
[B]
All attributes of X are having non null values