doubt

Question

For a relation to be in 3NF, being in 2NF is the necessary but not sufficient condition.   right or wrong   

can someone explain with example ?

Comments

It is necessary but not sufficient.

e.g.

Key->Nonprime

Nonprime->Nonprime

Consider  above FD in which, NP on LHS is not part of any key thus still in 2NF but not in 3NF

Answer 1

if a relation is in 3NF then the relation must be in 2NF . it is necessary and sufficient t condition .

A---->B is in 3NF then A is a key or B is a part of prime attribute . if it is in 3NF then partial dependency is never possible becz A is never become subset of key . and b never become non prime attribute otherwise it vialote the 3NF.