A queue is implemented using a non-circular singly linked list. The queue has a head pointer and a tail pointer, as shown in the figure. Let $$n$$ denote the number of nodes in the queue. Let $$enqueue$$ be implemented by inserting a new node at the head, and $$dequeue$$ be implemented by deletion of a node from the tail.

Which one of the following is the time complexity of the most time-efficient implementation of $$enqueue$$ and $$dequeue,$$ respectively, for this data structure?

Consider the following two tables and four queries in SQL.

Book (isbn, bname), Stock (isbn, copies)

Query 1:

SELECT B.isbn, S.copies
 FROM Book B INNER JOIN Stock S
 ON B.isbn = S.isbn;

Query 2:

SELECT B.isbn, S.copies
 FROM Book B LEFT OUTER JOIN Stock S
 ON B.isbn = S.isbn;

Query 3:

SELECT B.isbn, S.copies
 FROM Book B RIGHT OUTER JOIN Stock S
 ON B.isbn = S.isbn;

Query 4:

SELECT B.isbn, S.copies
 FROM Book B FULL OUTER JOIN Stock S
 ON B.isbn = S.isbn;

Which one of the queries above is certain to have an output that is a superset of the outputs of the other three queries?

In an Entity-Relationship $$(ER)$$ model, suppose $$R$$ is a many-to-one relationship from entity set $$E1$$ to entity set $$E2.$$ Assume that $$E1$$ and $$E2$$ participate totally in $$R$$ and that the cardinality of $$E1$$ is greater than the cardinality of $$E2$$

Which one of the following is true about $$R$$?

Consider the relations $$r(A, B)$$ and $$s(B, C),$$ where $$s.B$$ is a primary key and $$r.B$$ is a foreign key referencing $$s.B.$$ Consider the query

$$Q:$$ $$\,\,\,\,\,\,\,\,\,$$ $$r$$ $$\,\,\,\,$$ $$\bowtie$$ $$\,\,\,\,$$ $$\left( {{\sigma _{b < 5}}\left( s \right)} \right)$$

Let $$LOJ$$ denote the natural left outer-join operation. Assume that $$r$$ and $$s$$ contain no null values.

Which one of the following queries is NOT equivalent to $$Q$$?