SQL logic

Question

In SQL 3-Valued logic, what is the value of the following expression?
(x<y OR x≥y OR z=5)

1. TRUE or FALSE but never UNKNOWN
2. FALSE or UNKNOWN but never TRUE
3. TRUE or UNKNOWN but never FALSE
4. TRUE, FALSE or UNKNOWN

Answer 1

Let A = X<Y, then A' = X$\geq$Y
Now, A OR A' will always result in TRUE or UNKNOWN (if either X or Y or both are UNKNOWN)

Coming to Z = 5, it may be TRUE, FALSE or UNKNOWN
If Z = 5 is TRUE or FALSE, result will be TRUE or UNKNOWN depending on value of A OR A', but never FALSE.
If Z = 5 is UNKNOWN, result will be UNKNOWN. 

Hence, answer will be Option C.