In SQL, relation can contain null values, and comparisons with null values are treated as unknown suppose all comparisons with a null value are treated as false.
Which of the following pairs is not equivalent?
1
x = 5, not (not (x = 5))
2
x = 5, x > 4 and x < 6, where x is an integer
3
x ≠ 5, not (x = 5)
4
none of these