Question

Consider the following statements given below:
$S_1:$ In relational algebra join in a basic operation.

$S_2:$ If a functional dependency $A\to B$ holds in relation R(A, B, C) then AC $\to$ B also holds.

$S_3:$ In the WHERE clause of a SQL query the condition 'A' = NULL is evaluated to be false. How many number of above statements are true_______.

• A. 1

Answer 1

The correct option is A 1
$S_1:$ In relational algebra basic operations are $(\sigma ,\pi ,U,-,x,\rho )$. Join is not a basic operation because it can be derived from operations.

$S_2:$ R (A, B, C) it A $\to$ B holds than AC $\to$B holds $S_2$ is true.

$S_3:$ NULL in any comparrison can not be evaluate either TRUE or FALSE because NULL is not a value and we can not compare a value with a which is not a value $S_3$ is false.