gate 2000

Question

In sql relations can contain null values,and comparisons with null values are unknown. suppose all comparisons with a null value are treated as false. which of the following pairs is not equivalent ?                                      a.x=5,not (not  (x=5))                                        b.x=5,x>4 and x <6,where x is an integer       c.x <5,not  (x=5)                                                   d.NOT

Answer 1

Answer: C

As if x is considered NULL, and any comparison with NULL yields False.

Then, x <5 gives FALSE

not (x=5) --> not (False) --> True.

So They are not equivalent.

Comments

thanks:)