I want to know as we know codd's rule says that no two tuples in a relation should be same. i.e we can not have 2 tuples with same values in clm feilds. now to maintain these constraints, we choose to have some key over the relation which can uniquely identify relation. but we know that in SQL you can have 2 tuples with same values as this is the foundational block of multiset operations which we can perform in SQL. so my ques is SQL does not follow codd rule! right?? by this argument and if it does not follow, so in case of table having mutiset values, (as there are no keys present), how Dbms do indexing to retrive records?
someone help me on this pls.