An n $$\times$$ n array v is defined as follows V [i, j] = i - j for all i, j, $$1 \le i \le n,\,1 \le j \le n$$ The sum of the elements of the array v is

In SQL, relations 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?

Given relations r( w, x ) and s( y, z ), the result of

select distinct w,x
from r, s;

is guaranteed to be same as r, provided

Given the relations

employee (name, salary, deptno), and
department (deptno, deptname, address)

Which of the following queries cannot be expressed using the basic relational algebra operations $$\left(\sigma, \pi,\times ,\Join, \cup, \cap,-\right)$$?