In Oracle online docs (http://docs.oracle.com/cd/B19306_01/server.102/b14200/clauses002.htm), it's stated that :
To satisfy the constraint, each row in the table must make the condition either TRUE or unknown (due to a null).
What does the part of the sentence in bold mean? What I understand is that (since three value logic is implemented in Oracle DB) : to satisfy the constraint, each row in the table must make the condition either TRUE or NULL.
Am I correct or am I missing something?