Which statement is incorrect?

All data values of the primary key should be different in order to keep meeting primary

key constraint. That is$,$ if A$,$B$,$C are the attributes and $($A$,$B$)$ is a key, then tuples $(1,2,3)$ and

$(1,4,5)$ cannot be in the table simultaneously, since $1$ repeats

None of the data values of a primary key can be NULL as PRIMARY KEY constraint

implies NOT NULL fo

all data values of the primary key

No two data tuples should agree on the attributes included in the priman

An attribute of a primary key can also be used and referred to in a foreien key constraint